Tech calving

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Technote 1 Jan 2000

Technote 1Environmental exposure

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GReduce exposure toenvironmentalmastitis bacteria

1TECHNOTE

‘Environmental mastitis’ refers to intramammary infections caused by organismsthat survive in the cow’s surroundings – including in soil, manure, bedding, calvingpads, water, or on body sites of the cow other than the mammary gland. Infectionof the udder with these organisms is often opportunistic, taking advantage ofcircumstances that favour environmental contamination and changes in themammary gland’s susceptibility to infection. There are many bacteria in theenvironment and some have biological characteristics that enable them to multiplywithin the udder.

Most cases of environmental mastitis occur within a few weeks of calving, whenthe cows’ natural defence mechanisms are low and their udders have been incontact with mud and manure during calving. However, exposure of teat ends toenvironmental bacteria can occur at any time: before heifers have their first calf,during calving, at milking time or in paddocks during the lactation or dry periods.During lactation, factors that predispose cows to infection with environmentalbacteria include milking udders that are wet or dirty, or administeringintramammary infusions if the teat orifice is not sterile. During the early and latedry periods, absence of the keratin plug in the teat canal may make cows highlysuseptible to infection.

Bacteria that commonly cause environmental mastitis are Streptococcus uberis

or Escherichia coli. Other environmental organisms causing mastitis include othercoliform bacteria (Klebsiella species, Enterobacter aerogenes), Pseudomonas

aeruginosa, Bacillus cereus, Arcanobacterium (formerly Actinomyces orCorynebacterium) pyogenes, Serratia species, Nocardia species, Candida (yeast)and Protheca (algae). Characteristics of some of these bacteria are described inthe following tables.

Strep uberis usually responds to treatment but some cases can be difficult tocure. Coliforms do much of their damage through toxins released after the bacteriadie. Pseudomonas is virtually impossible to treat and cows that survive must beculled.

Streptococcus dysgalactiae has characteristics of environmental and cow-associated causes of mastitis and it is not easy to categorise. In Australia, Strepdysgalactiae is commonly seen in heifers before they start lactation. The bacteriacan be isolated from the environment and from sites on the animal such as themouth, udder and vagina. Infection can occur between milking from Strep

dysgalactiae in the cow’s environment or it may be spread between cows atmilking. Flies can physically spread the bacteria.

Technote 14.3 and 14.4 discussStrep uberis and blanket Dry CowTreatment.

✔

Mastitis is divided into two types– cow-associated andenvironmental. The bacteriacausing cow-associated mastitisusually reside in udder tissueand on teat skin and are mostcommonly spread at milking. Thebacteria causing environmentalmastitis survive in the cow’senvironment and, althoughmilking may facilitate their entrythrough the teat canal, theenvironment is the primarysource of infection.

Technote 5 describes characteristicsof common cow-associatedmastitis bacteria.

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Technote 1


Reservoir of infection

Spread

Cow susceptibility

Clinical signs

Characteristics of the common environmental mastitis pathogens

Characteristic Strep uberis Escherichia coli*

The bacteria is widespread in theenvironment.

In rare cases, udders of chronically infectedcows are a reservoir of infection and theirmilk may contaminate milking equipment.

Contamination of teat surfaces occurs in theenvironment.

Infection can occur at any time, includingduring milking.

Clinical cases are common in heifers andcows before and during calving, and in high-producing cows in early lactation. Downercows with milk fever paresis may be athigher risk.

Susceptibility is increased in cows withselenium or Vitamin E deficiency especially inthe two weeks either side of calving.

Most infections are mild and have waterymilk with small flakes.

The bacteria can cause a sudden and severetoxaemia where cows develop a hightemperature and may become recumbentand die. Milk from these cases can be ayellow, watery secretion with white flakesthat can turn bloody (brown) later.

Coliforms do not usually invade udder tissue– toxins cause the damage. Quarters oftenreturn to part production in the samelactation and full production the followinglactation.

The bacteria can be isolated from theenvironment, faeces and many sites on cows– especially the abdominal skin.

Some cows pass large numbers in theirfaeces.

The udders of chronic, subclinically infectedcows are a potential reservoir and their milkmay contaminate milking equipment.

Contamination of teat surfaces occurs in theenvironment.

Infection can occur at any time, includingduring milking.

Infection most frequently occurs in the firsttwo weeks of the dry period, and during thecalving period and early lactation, especiallyif there is teat end damage or oedema.

In the early dry and calving periods, changesin udder secretions, the lack of flushing atmilking, and the absence of the keratin plugin the teat canal make the cows highlysusceptible to infection.

Infection with Corynebacterium bovis maymake quarters more susceptible to Strepuberis (Hogan et al 1988).

About 50% of clinical cases have anenlarged, inflamed quarter and changes inthe milk. In about 40% of cases changes arevisible only in the milk. In about 10% ofcases the cows develop a fever and go offtheir feed.

Research indicates significant differencesbetween the ability of various strains of thebacteria to infect the udder. Some strains areprotected by bacterial capsules, some invademammary tissue and may resist naturaldefence mechanisms and the action ofantibiotics.

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Bacterial shedding in milk

Cell counts (ICCC)

Milk quality

Management during outbreaks

* Escherichia coli infection is often called ‘coliform mastitis’, which can also be caused by the less common but related bacteria Klebsiella spp and Enterobacter

aerogenes.

Most infections are short-lived but a smallpercentage become chronic (Hogan andSmith 1997).

Most infected cows have ICCC higher than500,000 cells/mL.

Bacteria are not usually found in vat milkunless there is a high prevalence of infectionin the herd.

Most isolations from vats are likely to be frombacteria on teat surfaces rather than fromudder infections.

Strep uberis can multiply in vat milkrefrigerated at 10°C.

Manage calving cows to minimise exposureto contamination. If possible, use sand ratherthan organic materials for calving pads.

Begin milking and disinfecting teats of cowstight with milk prior to calving, especiallythose leaking milk.

Improve pre-milking hygiene and considerpre-dipping teats before milking.

Examine milking machine functions(especially pulsation, liner length andvacuum).

Use blanket long-acting Dry Cow Treatmentat the next dry period to prevent newinfections.

Bacteria are shed in the first 6-12 hours ofclinical signs, and are reduced thereafter.

Most infections are of short duration – morethan 50% last less than 10 days. Some(1-2%) continue for more than 100 days.

Severe cases are nearly always culturepositive. Other cases are often culturenegative because the cows have alreadyeliminated the bacteria.

ICCC rapidly increase following infection andpersist for about two weeks, after which thebacteria are eliminated.

In chronic cases ICCC tend to be high (about500,000 cells/mL) although they canfluctuate.

Clinical and chronic coliform cases do notcontribute significantly to vat milkcontamination.

Most isolations from vats are likely to be frombacteria on teat surfaces rather than fromudder infections.

Manage calving cows to minimise exposureto contamination. If possible, use sand ratherthan organic materials for calving pads.

Begin milking and disinfecting teats of cowstight with milk prior to calving, especiallythose leaking milk.

Improve pre-milking hygiene and considerpre-dipping teats before milking.

Overseas, vaccination with J-5 vaccine in thedry and early lactational periods reduces theincidence and severity of many of thecoliform infections. This vaccine is notregistered for use in Australia.

Characteristic Strep uberis Escherichia coli*

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Technote 1


Characteristic Pseudomonas Arcanobacterium Bacillus cereus Nocardia species aeruginosa pyogenes

Characteristics of some less common environmental mastitis pathogens

Reservoir of infection

Spread

Cow susceptibility

Clinical signs

Bacterial sheddingin milk

The bacteria is common inthe environment – inplaces such as watersources and ponds. It cancolonise water hose andhot water systems and isresistant to somesanitisers.

Infection may beintroduced into the udderwith intramammarytreatments if teat ends arenot dried or preparedaseptically.

Spread is fromcontaminated water –either in the environmentor water used to washudders.

Cows are susceptibleduring milking andwhenever udder infusiontakes place.

Cases range from mild to asevere acute form withsepticemia and death.Secretion varies, but maybe a brown serum.

Affected cows do notrespond to treatmentregistered for use in cattle.

If infection occurs at DryCow Treatment, clinicalsigns may not be seenuntil the next calving.

Generally low numbers ofbacteria are shed, withintermittent shedding inchronic cases.

The bacteria is common inthe environment.

Occasional individualcases may be associatedwith teat or udder injury.

This bacteria is one of amix of bacteria causing‘summer mastitis’described in Europe andpossibly spread by bitingflies.

Dry cows and heifers priorto first calving aresusceptible to infection.

Infection commonlycauses a severe mastitis.Typically the cow is sick,the quarter is hard, theteat is often very swollen,and secretions consist ofthick pus with a putridsmell.

Function may bepermanently lost inaffected quarters and teatobstruction followinginflammation is common.

Cases are usually clinicaland large numbers ofbacteria are passed in thesecretion.

The bacteria is common inthe environment andforms heat- andchemical-resistant spores.


Mastitis has beenassociated with feedingbrewer’s graincontaining spores.

Susceptible during uddertherapy.

Mild to peracute forms.Haemorrhage andgangrene can occur.

If infection occurs at DryCow Treatment, clinicalsigns may not be seenuntil next calving.

Cases are usually clinical.

The bacteria is commonin soil.

It can also survive inchlorhexidine teatdisinfectant.


Spread can be bycontaminated water usedto wash udders or incontaminated teatdisinfectant. Spread fromcow to cow at milking ispossible.

Infection occurssporadically.

Although cows aresometimes sick, infectionis rarely fatal.

Affected quarters areusually swollen or hardwith lumps. Secretions aregrey and viscid with small(1 mm) white flecks.Lumps may rupture anddischarge to the surface.Infected cows do notrespond to treatment.

WARNING: Take carewhen handling infectedcows as Nocardia speciescan cause respiratoryinfections in people.

Bacteria in fresh milk maynot survive refrigeration orfreezing of sample.

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Cell counts

Milk quality

Management duringoutbreaks

Cell counts are generally>500,000 cells/mL inchronic infections.

Milk supply can becontaminated by watersources. This bacteria maycause milk spoilage.

It is important to assessthe intramammarytechnique being used andmanagement of cowsimmediately aftertreatment.

Affected cows do notrespond to availableantibiotics.

Culture of water sources isoften unrewarding, whilechanging water hoserubberware is often useful.

Water supply for teatdisinfectants should beheated to 70°C or aboveand cooled before use.

Identification of infectedquarters may requirerepeated culture.

Positive cows should beculled.

Cases are usually clinicalwith very high cell counts.

Cases are usually clinicaland their milk is excludedfrom the vat.

In countries where‘summer mastitis’ iscommon, carefulmanagement during thedry period (e.g. locatingcows in low riskpaddocks) is essential. Itcan occur in areas withhot, humid summers (e.g.on the north coast of NewSouth Wales).

Consider blanket Dry CowTreatment if this is a herdproblem.

Fly control is also veryhelpful.

Cases are often clinical.

Bacteria can be recoveredfrom the bulk tank. Thisrepresents a potential milkquality hazard because theorganism may not bekilled by pasteurisation.


Affected cows do notrespond to availableantibiotics.

Culture of water sources isoften unrewarding.

Assess the sterility of teatdisinfectant.

Infected cows should beculled.

WARNING: Humaninfections are possible.




Characteristic Pseudomonas Arcanobacterium Bacillus cereus Nocardia species aeruginosa pyogenes

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Technote 1


1.1 Calve on clean, dry pasture or a clean,

dry calving pad.

The udder is very susceptible to infection at calving, and many infections detectedin early lactation are established at calving (Hogan and Smith 1998).

The ideal place for cows to calve is a clean, sheltered, dry area. The ideal situationis a paddock with a good cover of grass, not irrigated or contaminated withmilking shed or feed pad effluent, on an elevated site that is not wet, boggy orpoorly-drained. Unfortunately, such areas are rare on most Australian dairy farmsand most farm managers choose to use calving paddocks where the cows caneasily be supervised or calving pads, especially in areas of high rainfall duringthe calving period.

Calving paddocks can work if they are large enough so that grass cover ismaintained. However, it is common for small areas, which perhaps provide shelter,to be overused and become boggy. The only practical solution is to fence offsuch areas until they regenerate. If electric fences are shifted across a paddock atregular intervals, clean areas can be provided for new batches of calving cows. Itis important to avoid ‘back-grazing’ (where cows have access to recentlycontaminated areas in addition to their new area). Some planning is needed tocreate access lanes and allow for access to drinking water in each strip-grazingarea, for example by using mobile troughs. When cows are calving on grass it isalso important to ensure that preventative measures for metabolic diseases havebeen taken.

Calving pads can be a successful alternative for wet conditions. Drainage isprobably the most important factor and can be supplied by providing sufficientfall on the pad (of about 3-4%), or by installing underground slotted polyvinylchloride (PVC) pipe drainage on flat sites (Davison and Andrews 1997).

Usually some bedding material is provided to make the cows more comfortable.Organic bedding materials (straw, rice hulls, shavings or sawdust) support higherbacterial populations than non-organic materials (washed sand or groundlimestone). The particle size is also important. The surface area for bacterialgrowth and the chance of bacterial attachment and colonisation is increased infinely chopped or ground organic material. For this reason, long straw is generallybetter than finely chopped straw and shavings are better than sawdust (Hoganand Smith 1998).

Sawdust and other wood products tend to harbour the coliform bacteria and strawmay contain large numbers of environmental streptococci, such as Strep uberis(Bramley 1982, Smith and Hogan 1997). Sawdust may have high pathogen(Klebsiella species) counts even when fresh (Hogan et al 1989). Kiln-driedsawdust is less of a problem. Sawdust can be used satisfactorily provided it isstored dry and managed correctly (Blowey and Edmonson 1995). Pathogen countsare much lower when contaminated sawdust is removed and replaced with freshsawdust daily rather than weekly (Bramley 1992). Sawdust should not be used asbedding if it cannot be kept dry.

Confidence – High

Local observations of the importance ofhygiene in calving areas are consistentwith overseas research and experience.

Research priority – Moderate

Further information on what constitutes asuccessful calving pad surface, includingmeasurement of pathogen counts, couldbe useful.

✔

If possible heifers should becalved separately from the adultherd. Heifers are more likely tobe bullied and be forced to calvein the less suitable areas ofthe calving paddock orcalving pad.

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Technote 1 Jan 2000


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GAll bedding materials (organic and inorganic) will support high pathogen countsafter becoming contaminated with manure (Blowey and Edmonson 1995). Thearea must be kept well drained and contaminated material removed and replacedon a regular basis. Pathogen counts will be high before the bedding looks soiled,and chemical disinfection (agricultural or hydrated lime, formalin, etc) ofcontaminated bedding is not effective (Hogan and Smith 1998).

The recommendations that no more than two pats of manure are present persquare metre and no water is visible in foot prints are crude estimates designedto focus farmers’ attention at least on gross contamination, given the lack ofother more sophisticated monitoring techniques. Checking for fresh liquid manure,rather than dried pats, gives an indication of recent faecal contamination.

Practical and economic factors influence the surfaces available for calving cowsand must be individually assessed for each farm.

Options for surface types, inpreferred order (highest tolowest) are:

• clean, grassed paddock withno surface water;

• well-drained inorganic material,such as sand;

• well-drained organic material;or

• poorly drained calvingpaddock (a last resort). ✔

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Technote 1


1.2 Be alert to the number of cases of mastitis

occurring, especially in freshly calved heifers. This

is an indicator of the state of the paddock.

Mastitis in freshly calved heifers (first calvers) may result from infection thathas occurred during their development since puberty or in the few weeksimmediately before calving.

Heifers may be particularly susceptible to infection during the calving period.This is because they tend to spend longer calving, especially on the ground, andthey often suffer from some degree of udder oedema that may reduce the abilityof the teat and udder tissues to resist bacterial challenge (Slettbakk et al 1995).Field observations indicate a greater tendency of animals with oedematous teatsto develop Strep uberis infections.

Clinical mastitis was observed at calving in 8% of first-calf heifers in a study of11 herds in New Zealand (Pankey et al 1996). Environmental streptococci wereisolated from 68% of these clinical cases.

The warning index of three or more cases in the last 50 calvings is an estimatebased on the average incidence of clinical cases observed in the first month oflactation. Data on the incidence during the calving period (two weeks before andtwo weeks after calving) would allow this index to be refined, but it serves as areasonable guide. It is probably of more relevance in seasonal herds whererelatively large numbers of calvings occur over a short period (and 50 calvingsmay occur in as little as 1-2 days).

If this index is exceeded a reassessment of the calving environment andmanagement should be made. It is often useful to have an independent adviserhelp with this to obtain the benefit of a ‘fresh pair of eyes’. It is also worth notingthat sometimes a high incidence of mastitis occurs at calving, even though theenvironment appears clean and dry. These may be infections that occurred at anearlier time (for example at drying-off) and then became clinical at calving.

Confidence – Moderate

This recommendation assumes that mostheifers enter springer mobs with a lowprevalence of infection.

Research priority – Low

Analysis of the timing of clinical cases ofmastitis, as part of the milk recordingstatistics, would provide better benchmarkinformation on new infection rates.

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Technote 1 Jan 2000


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1.3 Bring cows into the shed as soon as possible to

milk out and check – certainly within 24 hours of

calving.

In 1996 Pankey et al noted that many ‘over-conditioned’ heifers leaked milkprior to calving and had a higher prevalence of mastitis. They believed preferentialtreatment of heifers during the calving period may reduce the incidence of newinfections and suggested several factors to aid mastitis control in heifers including:• minimising exposure to muddy conditions;• milking them out as soon as possible after calving; and• applying an effective teat sanitiser after every milking.

In the past, preventive management of milk fever (a sudden reduction in thecalcium level in the blood) sometimes involved leaving milk in the udder offresh cows. This practice is now discredited because it predisposes to mastitis(O’Shea 1987). Rather than treating milk fever by incomplete milking, it shouldbe controlled by managing the diet before and at calving to manipulate calciumavailability in this period.

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Technote 1


1.4 Take special care with induced cows.

Long-acting corticosteroids (such as dexamethasone) are widely used to induceparturition in dairy cattle in parts of Australia. They can impair secretion ofproteins that are critical to normal cellular and humoral immune responses(Nonnecke et al 1997), an effect that is strongly linked with changes in thecomposition of the white blood cells. The ability of cows to respond to stressorsmay be reduced by the use of long-acting corticosteroids to induce prematurecalving.

Browning et al (1990) describe a collapse syndrome associated with the use ofdexamethasone for inducing calving. It appeared to result from gram-negativeendotoxaemia associated with subclinical infections as three of the seven cowsin this study had peracute Escherichia coli mastitis confirmed at post-mortemexamination.

Immune suppression resulting from the use of long-acting corticosteroids toinduce parturition is still profound at the time of parturition. Steps must be takento minimise exposure of induced cows to mastitis-causing pathogens at this time.

Confidence – High

Field experience in Australia shows thatinduced cows are more susceptible toEscherichia coli infection.


To minimise the risk of environmental mastitis in induced cows,practitioners recommend the following procedures:

• Maintain cows in clean, well-drained paddocks (the best calving areaavailable on the farm) from the time they receive their first injection toinduce parturition until after they have calved.

• Milk cows once the udder is tight with milk. Induced cows often bag-uptightly before calving and may drip milk. Machine milking isrecommended once the udder gets tight with milk, even though the cowmay not yet have calved. “If she’s dripping milk, she should be milking.”

• Watch udders carefully for signs of mastitis. Some cases can be rapidand severe with few initial changes or abnormalities in the milk (e.g.water milk, clots or flecks).

• Monitor induced cows very closely for signs of systemic illness. Cowsmay become acutely ill with an Escherichia coli mastitis endotoxaemia,even though visible changes in the udder may be limited and thesecretion from the affected quarter is difficult to differentiate fromcolostrum. ✔

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G1.5 Take care with pre-milking preparation of udders.

Technote 5 describes good milking technique and the importance ofconsistent routine.

Key papers

Blowey R, Edmondson P. The environment and mastitis. In: Mastitis control in dairy herds, Chapter

8, Farming Press Books, Ipswich, United Kingdom, 1995:103-118.

Bramley AJ. Bovine Medicine. Blackwell Science Publications, Oxford, United Kingdom, 1992.

Bramley AJ. Sources of Streptococcus uberis in the dairy herd. I. Isolation from bovine faeces and

from straw bedding of cattle. J Dairy Res 1982;49:369-373.

Browning JW, Slee KJ, Malmo J, Brightling P. A collapse syndrome associated with gram-negativeinfection in cows treated with dexamethasone to induce parturition. Aust Vet J 1990;67:28-29.

Davison TM, Andrews RJ. Feed pads down under. Department of Primary Industries, MutdapillyResearch Station, Queensland, 1997.

Hogan JS, Smith KL, Hoblet KH et al. Bacterial counts in bedding materials used on nine commercialdairies. J Dairy Sci 1989;72:250-258.

Hogan JS, Smith KL. Occurrence of clinical and subclinical environmental streptoccal mastitis. In:Proceedings of the symposium on udder health management for environmental streptococci,

Ontario Veterinary College, Canada, 1997;36-41.

Hogan JS, Smith KL. Risk factors associated with environmental mastitis. In: Proceedings of the

37th National Mastitis Council Annual Meeting, St Louis, Missouri, 1998:93–97.

Hogan JS, Smith KL, Todhunter DA, Schoenberger PS. Rate of environmental mastitis in quartersinfected with Corynebacterium bovis and Staphylococcus species. J Dairy Sci 1988;71:2520-

2525.

Nonnecke BJ, Burton JL, Kehrli ME. Associations between function and composition of blood

mononuclear leukocyte populations from Holstein bulls treated with dexamethasone. J Dairy

Sci 1997;80:2403-2410.

O’Shea J. Machine milking factors affecting mastitis. In: Machine milking and mastitis, Bulletin of

the International Dairy Federation No. 215, Brussels, Belgium, 1987:25-27.

Pankey JW, Pankey PB, Barker RM, Williamson JH, Woolford MW. The prevalence of mastitis in

primiparous heifers in eleven Waikato dairy herds. NZ Vet J 1996;44:41-44.

Slettbakk T, Jorstad A, Farver TB, Holmes JC. Impact of milking characteristics and morphology of

udder and teats on clinical mastitis in first- and second-lactation Norwegian cattle. Prev Vet Med

1995;24:235-244.

Smith KL, Hogan JS. Risk factors for environmental streptococcal intramammary infections. In:

Proceedings of the symposium on udder health management for environmental streptococci,Ontario Veterinary College, Canada, 1997;42-50.

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Technote 1


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Technote 2 Jan 2000

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Take care with two-year-oldand freshly calved cows

It takes about two weeks for most heifers to establish a quiet, reliable response tomilking. To maximise production and minimise risk of injury to milkers andanimals, milking staff must be patient and as gentle as possible during this period.

Extra labour may be required for the calving period in seasonal herds.

2.1 Consider training heifers in the milking area

before calving.

&

2.2 Take your time moving and milking two-year-old

cows and freshly calved cows – don’t rush.

Technote 5.1 describes how to ensure cows enter the milking shedwillingly.

2.3 Attend to two-year-old cows with severe udder

oedema (also known as ‘flag’).

Udder oedema is a swelling that occurs under the skin of the udder, and sometimesalong the belly, in cows prior to calving. It mostly occurs in heifers at their firstcalving, but can occur at subsequent calvings, and is commonly observed duringlate pregnancy and early lactation.

In severely affected animals, milking is a painful process, milk let-down is poor,and susceptibility to infection is increased (Slettbakk et al 1995). Field experiencesuggests that animals with severe oedema are more likely to rupture suspensoryligaments of the udder causing permanent damage, known by farmers as ‘droppedudder’ or ‘blown bag’.

Oedema largely results from compromised fluid drainage from the udder and thesurrounding areas. A small amount of oedema is a normal (physiological)occurrence as the blood supply to the udder increases and changes during theperiparturient period.

Confidence – High

Severe oedema can result in long-termstructural damage to suspensoryligaments of the udder.


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Technote 2

Technote 2Fresh cows

In most cases the oedema disappears within a day or two of calving but, in severecases, it can interfere with milking. Once milking is started, the volume of theudder is reduced and oedema fluid is usually cleared.

Veterinary advice should be sought if cows are very uncomfortable.

Diuretics used prior to calving are less effective – possibly because of the largevolume of foetal fluids present.

Factors that may lead to numbers of animals with udder oedema or increasedseverity of cases include excessive feeding immediately prior to calving, excessivedietary sodium or potassium, overfat heifers, and a hereditary predisposition tooedema. Advice on heifer nutrition should be sought to ensure diet does notcontribute to severe flagging.

2.4 Ensure all quarters of all cows are milked out.

Technote 5.8 describes under milking.

Key papers

Slettbakk T, Jorstad A, Farver TB, Holmes JC. Impact of milking characteristics and morphology ofudder and teats on clinical mastitis in first- and second-lactation Norwegian cattle. Prev Vet Med

1995;24:235-244.

Prior to calving, options for treating cows and heifers with oedema include:

• milk them out, save the colostrum for their calves, and commenceregular milking; or

• induce calving (especially if natural calving is not expected for sometime), making alternative arrangements to provide colostrum to the calf.

After calving, treatment of oedema involves frequent milking and the use ofeither:

• injected diuretics; or

• oral combinations of diuretic and dexamethasone. ✔

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Technote 3 Jan 2000

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Technote 3Vat check

3TECHNOTE

Check that milk issuitable to go in the vat

For milk quality reasons, all cows must have their colostrum milk withheld fromthe vat for at least eight milkings after calving. Colostrum may be present forlonger in induced cows, and milk should be withheld from the vat for at least 10milkings.

Antibiotic withholding periods for milk, cull cow and calf meat need to beobserved for cows that received Dry Cow Treatment (DCT).

3.1 Ensure each cow has exceeded her Dry Cow

Treatment Minimum Dry Period before putting her

milk in the vat or selling her calf.

Dry Cow Treatments are antibiotic preparations that are infused into each quarterof the udder immediately after the last milking of a cow’s lactation. Theformulations are designed to remain in the udder in concentrations high enoughto kill mastitis bacteria for relatively long periods (20-70 days depending on theproduct used).

Withholding periods

Generally, withholding periods refer to the minimum period of time that mustelapse between the last treatment of an animal with a veterinary medicine andthe supply of products (meat or milk) from those animals for food consumption.After treatment with a medicine, the length of time that meat must be withheld isusually longer than the withholding period for milk.

When using intramammary Dry Cow Treatments in the herd, there are twoprinciples relating to withholding milk that must be well understood:• All Dry Cow Treatments are registered with a specified Minimum Dry Period

after treatment. This is the minimum time that must elapse betweenadministration of the treatment and calving.

• As well as a Minimum Dry Period, all Dry Cow Treatments have recommendedwithholding periods for milk.

Confidence – High

The Minimum Dry Period for Dry CowTreatment is a stipulated requirement tosatisfy international and domesticstandards for food purity.


Assessment of antibiotic residue in calvesmay warrant research.

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Technote 3

Technote 3Vat check

For milk:• The withholding period for milk refers to the time that must elapse after calving

(rather than after treatment) before milk is supplied for processing.• A different withholding period for milk applies if the cow calves before the

Minimum Dry Period has elapsed (see table following page).

For cull cow meat:• The withholding period for meat applies from the date that the cow is treated

with Dry Cow Treatment.

For bobby calf meat:• There is no meat withholding period specified for calves born after the

Minimum Dry Period – although at least four days must elapse between theirbirth and slaughter for welfare reasons.

• Calves born before the Minimum Dry Period has elapsed are subject to thesame meat withholding period stated on the label for the cow. The withholdingperiod starts from the date that the cow was treated if the calf has not sucked orfrom the date of the calf’s last suckle, if it has sucked.

The likelihood of antibiotic residue in bobby calf meat depends on (1) theabsorption of antibiotic from the mother’s bloodstream (Rangel-Lugo et al 1998)and (2) the intake of antibiotic from colostrum. Limited information is availableon antibiotic residues in calves born to cows given Dry Cow Treatment. To protectthe $2.6 billion Australian beef industry, withholding periods for calves areinterpreted conservatively to minimise the risk of residue because there is nosubstantial set of research data on Dry Cow Treatment residues in calves. Thesafety net gives rise to markedly different actions for bobby calves born beforethe Minimum Dry Period according to whether or not they have suckled, howeverthere is no information on whether these actions are necessary from a biologicalpoint of view. For calves born after the Minimum Dry Period has elapsed, thecow’s colostrum will only contain traces of antibiotic (if any) and absorption ofmost Dry Cow Treatment antibiotics from the calf ’s gut is relatively poor.

Remember:

• If cows calve early or a decision to cull them during the dry period ismade, the date of treatment and the withholding period of the particularproduct must be known.

• Recommended withholding periods for milk and calf meat are longer ifcows calve before expiry of the Minimum Dry Period.

• Ensure that the ‘dry cow’ paddock is well away from the milking herd sothat cows given Dry Cow Treatment cannot accidently rejoin the milkingherd.

• Dry cows should be clearly marked.

• If there is any possibility that milk may contain antibiotic residue, itshould be withheld from the vat. ✔

✔

Farmers should not restrict thecolostrum intake of calves duringthe first 12 hours after birthdespite the possibility of havingto keep some calves for a longerperiod before sale. Healthand survival rates aresignificantly depressed incolostrum-depleted calves.

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Technote 3Vat check

Advisers should check the NRAweb-site for up-to-dateinformation on registered DryCow Treatment products:www.dpie.gov.au/nra

Technote 14.5 describes the activeingredients and spectrum of activityfor these products.

Technote 4.10 describes tests forantibiotic residue.

When Dry Cow Treatments are used according to directions on the label and theappropriate Minimum Dry Period and withholding periods are observed, antibioticresidues will not exceed Australian Maximum Residue Limits. (Organisationsresponsible for food safety, such as the National Regulatory Authority in Australia,set Maximum Residue Limits and they may vary from country to country.)

Each product has its own specified withholding periods.

Recommendations to minimise the risk of antibiotic residues in meat or milkafter use of Dry Cow Treatment are given in the Countdown Downunder FarmGuidelines for Mastitis Control Fact Sheet D and advisers should emphasisethese to their clients. A table of recommended withholding periods for Dry CowTreatments is repeated below, including some minor updates (current for October1999).

✔Recommended withholding periods for milk and meat (days) following use of each Dry Cow Treatment(October 1999). Withholding period – WHP; Dry Cow Treatment – DCT; Minimum Dry Period – MDP.

CULL COW MEAT MDP MILK CALF MEATWHP after date WHP after date In cows that calve

of DCT of calving BEFORE the MDP

For cows that For cows that For calves that For calves that docalve BEFORE calve AFTER suckle – WHP not suckle – WHP

the MDP the MDP after the calf’s after date oflast suckle dam’s DCT

Ampiclox Dry Cow 30 30 10 96 hours* or 30* 30*8 milkings

Cepravin Dry Cow 21 56 Test after 96 hours or 21* 21*4 days* 8 milkings

Elaclox DC 30* 30* 21 * 96 hours or 30* 30*8 milkings

Elaclox DC Xtra 30 35 21 * 96 hours or 30* 30*8 milkings

Noroclox Dry Cow 30 30 30 96 hours* 30* 30*

Orbenin Dry Cow 30 30 21 96 hours or 30* 30*8 milkings

Orbenin Enduro 30 35 21 * 96 hours or 30* 30*8 milkings

Figures with an asterisk are not from material approved by the National Registration Authority, but provided by the pharmaceutical companies as consistent with

NRA-approved withholding periods for other products. Contact the manufacturer or a veterinarian for further information.

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Technote 3

Technote 3Vat check

Confidence – High

Exclusion of colostrum from the vat ismotivated by factory standards for milkquality and is reflected in milk payments.


3.2 Ensure that milk from the colostrum phase

(first eight milkings) is not included in the vat

(at least 10 milkings for induced cows).

Colostrum or ‘first-milk’ is thick, yellow, and sticky and contains very highlevels of blood proteins (immunoglobulins, particularly IgG1) that help protectnewborn calves against disease.

These immunoglobulins are actively transported from the cow’s blood into themammary secretion during the eight weeks prior to calving. The first colostrumcan have an IgG1 concentration more than 100 times greater than normal milk.Following each milking, the pool of IgG1 in the udder is steadily lowered untildepleted.

Colostrum also contains high numbers of somatic cells. The high influx of whiteblood cells into the udder at this time is generally not due to mastitis (bacterialinfection) but is a response to some tissue damage as lactation begins. Thesecells have associated high levels of enzymes that can degrade milk solids.

Colostrum has a significant effect on the processing efficiency of all dairyproducts when levels are greater than 0.3% IgG1.

Because the concentration is so high in first-milk, the milk of only two cows inthe first 48 hours of lactation may be sufficient to raise the level of theconsignment above 0.3% IgG1 even when it is diluted with milk from 100‘normal’ cows.

Changes in product quality which occur at greater than 0.3% IgG1 include:• Butter – a darker colour, ‘off ’ flavours and downgrading.• Casein – decreases in yield due to changes in curd characteristics and poor

setting.• Cheese – increases in setting times, poor set, decreases in yield due to lower

casein levels, ‘off ’ flavours, shorter shelf life due to high moisture retentionby globular proteins, and body defects.

• Condensed milk – graininess.• Cottage cheese – agglutination of starter bacteria.• Milk powders – increases in drying times due to high moisture retention in

globular proteins, and difficulties in achieving a standard product.• Pasteurised milk – cream plugs.• UHT milk – shorter shelf life and deposit.• Whey – poor crystallisation due to altered composition.

Milk from the ‘colostrum mob’of cows is a good source ofnutrient for replacementheifers. ✔

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Technote 3Vat check

There are also significant cleaning problems associated with processing colostralmilk in the factory. It requires more frequent and more comprehensive cleaningof all heat transfer surfaces, increases the down-time on factory dryers andevaporators, and increases chemical usage.

Reducing colostrum levels in milk has made very significant improvements inprocessing milk to manufactured products. For example, after Bonlac Foods Ltdintroduced colostrum testing and included colostrum in their milk quality paymentscheme in 1993, farm level compliance markedly increased and products couldbe made to export specification 2–3 weeks earlier than was previoulsy possible.

Depletion of colostrum in milk after calving

IgG1 levels of up to 15% in the first colostrum fall to minimum levels of 0.15%by about eight days after calving. Levels of 0.3% and less are usually attainedafter eight complete milkings. Cows milked prior to calving after receivinginduction therapy also have high levels of IgG1, and levels don’t fall to under0.3% until after at least 10 full milkings (Auldist et al 1993).

Example of IgG1 concentrations in milk after calving (Rogerset al 1992)

In the past, farmers have visually appraised milk colour to ascertain when thecolostrum phase has finished. This is not sufficiently reliable because milk thathas lost its initial yellow-brown colour and looks white may still containunacceptably high levels of colostrum. The converse may also be true. Milk fromsome cows or herds may be coloured for reasons such as high levels of beta-carotene in pastures or because the milk comes from Jerseys rather than Friesians.

Key papers

Auldist MJ, Coats S, Rogers GL, McDowell GH. Characteristics of mammary secretion during

early lactation from naturally-calving dairy cows and cows induced to calve prematurely. Aust J

Dairy Technol 1993;44:49-52.

Rangel-Lugo M, Payne M, Webb AI, Riviere JE, Craigmill A. Prevention of antibiotic residues in

veal calves fed colostrum. J Am Vet Med Assoc 1998;213:40-42.

Rogers G, Coats S, Auldist M. Raw milk quality and product quality. In: Dairy Research Foundation

dairy symposium proceedings, Camden, July 1992:16-27.

You cannot assess milk quality byvisual appraisal. It is moreappropriate to withhold milk forthe recommended number ofmilkings and to ensure thatudders are beingcompletely milked out. ✔

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Technote 3

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Technote 4 Jan 2000

Technote 4Fresh cow clinicals

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✔

4TECHNOTE

Rapidly find, treat andrecord clinical casesin fresh cows

Clinical cases of mastitis are costly and severely disrupt the flow of milking.Cases that are missed can markedly increase the Bulk Milk Cell Count (BMCC)because they produce very high numbers of somatic cells in their milk.

The number of clinical cases detected within a herd is a function of the intensityof observation, and advisers therefore need to be aware of how different operatorsdetect mastitis. People who forestrip are likely to identify many more cases thanthose relying solely on observing a swollen quarter.

Early detection and treatment of all quarters with clinical mastitis reduces therisk of severe and intractable cases developing, and reduces the likelihood ofinfection being passed to other cows.

The Countdown Downunder warning level of “five cases per 100 cows in thefirst month of lactation” is based on diagnosis of mastitis following observationsof heat, swelling, pain, abnormal walking, poor milkout, or intense observationfollowing discovery of clots on the milk filter. This is typical of dairies in Australiawhere there is minimal pre-milking teat handling by the operator. In contrast,farmers who routinely forestrip will commonly identify cows with abnormalitiesin the first squirt of milk, followed by milk that is visibly normal. These cowsshould not be counted towards the warning level or treated as clinical cases.

The cost of a clinical case of mastitis

The likely cost of each clinical case during early lactation is estimated to average$146 (see table over page). This assumes a milk price of 25 cents per litre, alabour cost of $20 per hour, and a reduction in milk yield of 3% (Gunn et al1998). The risk factors for mortality, culling and vat contamination are estimatesbased on general experience.

Technote 10 details how to rapidlydetect and treat clinical cases inlactating cows.

Countdown Downunderconsiders a cow to have clinicalmastitis and require treatmentwhen there is observableabnormality of the milk(wateriness or clots) thatpersists for more than threesquirts of milk.

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Technote 4


Cost of treatment $Intramammary antibiotics = 10Vet visit and drugs @ $80 for 1 in 15 cases = 5Extra time in the shed 10 min/milking for 6 milkings @ $20/hr = 20

Discarded milk7 days of 20 L/day @ 25 cents/L = 35

Decreased yield for remainder of lactationFor cases in early lactation (calving to 30 days) estimated 3%reduction in 300 day yield of 5,000 L is 170 L @ 25 cents = 43

Risk of mortality1 in 200 cases, cow value $800 = 4

Risk of culling7 in 100 cases, replacement cost $400 = 28

Risk of contamination of vat2,000 L in 1 in 1,000 cases = 1

Total = $146

Calculating the cost of a clinical case in the first month of lactation

This cost would be higher for mastitis cases occurring in mid-lactation, as Gunnet al (1998) estimated that the 300-day yield of pasture-fed cows with clinicalmastitis was:• 3.4% lower than cows without mastitis if it occurred in early lactation (calving

to 30 days);• 7.7% lower if the mastitis in mid (peak) lactation (31 to 100 days post

calving); and• 2.0% lower for cases occurring in late lactation (101 or more days post

calving).

Using these figures, clinical mastitis in a herd of 150 cows is estimated to costabout $1,800 in the first 100 days of lactation. This is based on quarter infectionrates observed in Gippsland of 0.072 (72 clinically affected quarters per 1,000cows) in the first 30 days after calving and 0.007 (seven clinically affected quartersper 1,000 cows) between days 31 and 100 (Gunn et al 1999).

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pain in all freshly calved cows.

The signs and techniques used to detect clinical mastitis are the same throughoutlactation.

All freshly calved cows should be visually inspected for swollen quarters duringthe first two weeks after calving. Cows at high risk of mastitis should continue tobe closely examined as the lactation progresses. These include cows that:• have not milked out;• have had a clinical episode of mastitis within the last month; or• have recently had high Individual Cow Cell Counts (ICCC).

Cows that have swollen or painful quarters may appear lame – and this may bethe first indication of a mastitis problem.

People who put cups on and take cups off should be inspecting every cow forswollen quarters at every milking. When viewed from behind, the two hind-quarters should be examined for size and symmetry. In cows that have just calved,it can be difficult to pick swollen quarters and the best policy is to compare thesuspect quarter with other quarters. In thorough inspections, forequarters can beviewed by lifting the hindquarters.

Freshly calved cows with suspect quarters by gross observation should have theirudders palpated and foremilk checked.

Suspect udders should be palpated when they are empty after milking. The teat ispalpated with the finger tips by gently rolling it between the thumb and first twofingers, and glandular tissue is palpated superficially and deeply with the flat ofthe hand and fingers (Donovan et al 1992). The udder tissue of acute cases maybe hot, swollen or painful. In acute or chronic clinical mastitis cases with lessobvious changes, a thorough examination is required to assess the consistency ofudder tissue. Chronic changes usually manifest as fibrosis, which can be felt asfirmness that is local (from pea to fist size) or diffuse (giving the quarter a firmerfeel than its opposite number and usually a more nodular surface). Long-standinginfections can ultimately result in atrophy (shrinking) of the mammary tissue asit becomes non-functional.

Foremilk inspections are used to detect wateriness of the milk, a few clots orflecks, or more obvious abnormalities such as flakes, discolourations andbloodstains. Milking staff may see ‘strings’ of mastitis material hanging fromteat-ends. These are viscous debris (inflammatory products) that are expressedduring milking and may therefore be more obvious to the ‘cups-off’ operator.

Confidence – High

Heat, pain, and swelling are classicsigns of tissue inflammation.


Technote 5.2 describes foremilkstripping.

page 4

Technote 4


4.2 Check milk from all quarters of freshly calved

cows every day while they are in the colostrum

phase (first 8 milkings, or 10 milkings for induced

cows).

Technote 5.2 discusses foremilk stripping of cows during their colostrumphase.

Confidence – Moderate

Forestripping is the single most effectiveway to detect clinicals.

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Culture is the definitive method ofidentifying mastitis pathogens in herds– its cost is minor when compared topotential gains from incorporating theinformation into mastitis controlprograms.


4.3 Consider collecting milk samples for culture to

identify the bacteria involved.

The general principles of collecting milk samples for culture discussed in thissection are applicable to diagnosis of both clinical and subclinical mastitis, andalso as part of investigation of problems in herds.

Milk cultures are recommended whenever a herd problem emerges, namely whenthere are more clinical cases than is acceptable or when cell counts are rising.Virtually all mastitis is caused by bacterial infection. Milk cultures indicate thetype of bacteria in the herd (e.g. Staph aureus, Strep agalactiae or Strep uberis)so that appropriate management strategies can be developed. A number of milksamples are required to give a representative picture of what is happening in theherd (see below).

Culture costs vary from approximately $6 to $20 per sample depending on thenumber submitted at the same time, transport costs, etc.

Cultures of milk samples from clinical cases

It is not possible to determine the organisms responsible for a case of mastitiswithout culturing a clean milk sample.

Cultures from cases of clinical mastitis can provide useful information on:• Pathogen identification. This allows veterinarians and other advisers to use

their knowledge of the epidemiology of the organisms to suggest possiblesources of the infection and useful control measures for the herd.

• Antibiotic sensitivity testing of the isolated organisms. These tests are onlyconsidered as a guide to the likely treatment efficacy in live animals becausebacterial kill rates on sterile plates in a laboratory do not necessarily translateto curative treatment in inflammed udder tissue.

It is a good insurance policy to encourage farmers to take samples from all quarterswith clinical mastitis – although they won’t necessarily be submitted for culture.These should be collected before treatment (because the presence of antibioticsin samples make it difficult to grow bacteria) and stored frozen. The samples canbe submitted to a laboratory if:• a cow fails to respond to treatment;• there is concern about the type of bacteria causing the mastitis; or• there are a higher number of mastitis cases than expected (e.g. more than three

clinical cases in the past 50 calvings, more than five clinical cases per 100cows in the first month of lactation, or more than two cases per 100 cows permonth in subsequent months of lactation).

Sampling strategy

Aseptic technique must be used to collect milk samples from the type of casescausing concern, prior to administration of any treatment. For example, if theconcern is an outbreak of clinical mastitis in freshly calved cows, the samplesshould be taken from these clinical cases. Bacteria isolated from high cell countcows in the herd at the same time may not necessarily be relevant to the clinicalmastitis outbreak. Samples from cases that have recurred or failed to cure mayalso be unrepresentative of the overall problem.

Alternative methods for identifyingbacteria used overseas and inresearch are described in the‘Bacterial identification’ FAQ sheet.

In practice, it is only currentlypossible to determine thebacteria causing mastitis bydoing a milk culture. ✔

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Technote 4


The ‘Vat milk tests’ FAQ sheetdescribes bulk tank milk cultures.

• Advisers are encouraged tocopy and distribute Fact SheetA of the CountdownDownunder Farm Guidelinesfor Mastitis Control to clients.

• It is essential for advisers toensure the milkers’ samplingtechnique is satisfactory – aphysical demonstration is oftenvery helpful.

• On most farms it is the milkingstaff who collect milksamples from clinicalcases.

The number of milk samples to be examined depends on the number of cases ofmastitis occurring and the reason for the sampling. For most herd problemspreferably 10 samples (and a minimum of five) are needed to get a reasonablyreliable indication of the mastitis causing organisms in the herd. For large herds(more than 200 cows), it is preferable to have 20 samples. Between 10-40% ofsamples may return a result of ‘no growth’ (see below).

If a herd problem appears to recur some time later (certainly if more than 12months later), it is worth collecting another set of samples because herd profilescan and do change.

Recurring individual cases of clinical mastitis may have been ‘superinfected’with other bacteria such as Nocardia species or Pseudomonas introduced duringthe previous treatment infusion. This will only be detected if subsequent milksamples are cultured.

Sample collection

The main problems associated with milk culturing occur when samples arecollected and transported. If correct procedures are not followed, milk samplescan become contaminated with bacteria from water, mud or faeces, or from skin(milkers’ hands or cows). These environmental bacteria can multiply in the milksample and confuse the test result. Sterile sample collection and delivery of coolsamples to a laboratory within 24 hours, or immediately freezing the samplesafter collection and then later submission, avoids these problems.

Fact Sheet A in the Countdown Downunder Farm Guidelines for Mastitis Controlgives a detailed description of how to aseptically collect milk samples.

A milk sample should be considered contaminated if three or more colony typesare isolated from a quarter. The organism causing mastitis cannot be identifiedin contaminated samples. Contamination is often a result of poor sample collectiontechnique, a dirty environment or dirty animals. Teat injuries, wet teats or udders,and hands contaminated with milk or water are common causes of contaminatedmilk samples. Where possible, advisers should not arrange to take milk sampleson wet days or too soon after wet weather.

Storage and handling of milk samples

Most bacteria that cause mastitis survive refrigeration for several days or freezingfor several weeks. Nocardia species are an exception to this general rule, asstorage of samples for only a few hours or freezing can reduce the likelihood ofisolating these organisms. The survival of Staph aureus, Strep agalactiae, Strep

dysgalactiae and Strep uberis was not impaired in milk samples that were storedin a commercial freezer at –20oC for up to 16 weeks (Schukken et al 1989).Other studies have found a variable effect on streptococci, especially Strepdysgalactiae (Luedecke et al 1972, Murdough et al 1996).

The survival of Escherichia coli and Arcanobacterium pyogenes can also decreaseduring freezing, with recovery rates for both pathogens decreasing by about 20%in samples frozen for four weeks (Schukken et al 1989).

In a survey of the causes of clinical mastitis in East Gippsland, (Alison Gunnpersonal communication) there was a significant relationship between theproportion of samples from which no growth was obtained and the number of

✔

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Technote 4 Jan 2000


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days of storage (mostly in domestic freezers). She recommended that farmoperators should be encouraged to submit frozen milk samples for culture withina month of collection.

Freezing may increase the detection of coagulase negative staphylococci(Schukken et al 1989) and possibly Staph aureus. The proposed mechanism forthis increase is the release of intracellular bacteria after the destruction ofleucocytes during the freeze-thaw process. Samples found to have negative growthwhen cultured fresh may become positive after freezing.

Inappropriate storage and handling on-farm will significantly reduce the chanceof obtaining a meaningful culture result. It is not unusual to see samples sittingin the dairy for hours without refrigeration or on the dashboard of the car onFriday afternoon on the way to the veterinary clinic for submission to thelaboratory. It is essential for advisers to ensure the farm procedure for storingand handling samples is satisfactory – a physical demonstration is often veryhelpful.

Laboratory techniques

Techniques used in laboratories must be appropriate to achieve reliable isolationand identification of pathogens. This involves consideration of:• Methods of sample preparation, including warming and mixing especially

after freezing.• Possible pre-incubation in growth media.• The choice of culture media.• The methods of inoculating plates to ensure suitable combinations of

inoculum volume and surface area are used. Different combinations may beoptimal for different circumstances. For example, larger loop sizes holding25 µL or 50 µL would be appropriate for milk samples from clinical casescontaining less than 200 bacteria/mL, as the standard 10 µL loop is likely toresult in a culture with two or less colonies.

• Incubation temperature and times.• Procedures for follow-up of samples with ‘no growth’, including tests for

inhibitory substances, and examinations for other organisms.• Procedures and tests for identifying pathogens from the primary culture.• Procedures for antibiotic sensitivity testing.

At present in Australia there appear to be significant differences betweenlaboratories in techniques for bacterial isolation, characterisation and antibioticresistance testing, and there is no standard recording protocol. In addition tomajor laboratories, the number of small, local laboratories is increasing and manyof these are not using established quality assurance procedures. One objective ofCountdown Downunder is to establish uniform laboratory testing and reportingprocedures and to facilitate agreement by all laboratories to use them.

A bacteriology guide for bovine mastitis is published in the Australian StandardDiagnostic Techniques for Animal Diseases (Claxton and Ryan 1993). Althoughthis requires some updating, it provides a good start. In 1999, the National MastitisCouncil in the United States released a revised edition of its ‘Laboratory Handbookon Bovine Mastitis’. The handbook details microbiological diagnostic proceduresthat differentiate mastitis pathogens (National Mastitis Council 1999). Detailscan be obtained at its website at www.nmconline.org.

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Technote 4


Reasons for milk samples yielding ‘no growth’ after culture

Clinical cases of mastitis from which no growth is obtained are both commonand frustrating. Many published surveys of clinical mastitis report 10-40% ofsamples with no pathogen isolated. Probably the most common reason for ‘nogrowth’ is a decline in the number of bacteria in the sample, by the time it reachesthe laboratory, due to poor storage and handling. Other reasons include:• By the time the milk sample is collected, the infection has been eliminated by

host defence mechanisms. This is suggested particularly in the case ofcoli-form infections. Zorah et al (1993) found that 51% of ‘no growth’samples from clinical cases in Queensland were ELISA positive to Escherichiacoli antigens.

• Bacteria are present in too low a concentration to be detected by the laboratoryculture technique used. For example, the inoculum size used on culture platesmay be inadequate.

• Antibiotic treatment of the quarter before sample collection has interfered withthe ability to culture the infective organism. When submitting milk samplesfrom cows that are not responding to treatment or are repeat cases, it should benoted on the laboratory submission form if they have received antibiotics withinseven days of sampling.

• Contamination of the sample with disinfectant at the time of collection hasinterfered with the ability to culture the infective bacteria.

• The pathogen may not grow under normal culture conditions. For example,standard bacterial culture conditions are unsuitable for the detection ofobligate anaerobes, mycoplasma and fungi.

• The clinical signs of mastitis are due to non-bacterial causes such as toxicsubstances.

• Isolated bacteria may not be reported because they are not considered to bemajor mastitis pathogens. For example, coagulase negative staphylococci aretraditionally considered minor pathogens although they have been reported tocause clinical mastitis (Timms and Schultz 1987).

Antibiotic susceptibility testing

The disc-diffusion antibiotic sensitivity test (Kirby-Bauer method) is mostcommonly used in veterinary laboratories. The disc-diffusion method involvesinoculating an agar plate with a standard inoculum, adding discs containingstandardised quantities of antibiotics, incubating for 18 hours and measuring thezones of inhibition. In disc-diffusion tests, isolates are reported as susceptible,intermediate or resistant to the antibiotics that were tested. Many of the discs inuse were designed in human laboratories and some drugs listed on the antibioticsensitivity report may not be registered for use in cattle.

The fact that an antibiotic is found to inhibit growth in the laboratory does notnecessarily mean that it will be successful in curing infections from the udder.However, antibiotic sensitivity testing does give an indication of which drugs areNOT likely to be effective (Ziv 1997).

Antibiotic sensitivity tests showwhich drugs are not likely to beeffective. Just because anantibiotic is effective at killingbacteria on agar plates in thelaboratory does not mean itwill have the same successin the cow. ✔

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veterinarian.

The goal of treatment is to cure the infection (bacteriological cure), return theaffected mammary glands to normal milk production (clinical cure), and minimisepain and suffering of the cow. Ideally, the treatment period should be as short aspossible and there must be no risk of antibiotic residues entering the milk vat.

Staphs or Streps cause more than 80% of clinical mastitis cases in Australia.

Antibiotics are the basis of most treatment regimens and are administered byinfusion into the affected quarter (intramammary route) or by intravenous,intramuscular or subcutaneous injection (parenteral or systemic routes).

Other support therapies such as oral or intravenous fluids and anti-inflammatoriesmay be used in very severe cases. Frequent stripping out and use of oxytocin toaid milk let-down are important adjuncts. Farmers should always be encouragedto remove milk from mastitic quarters, despite the fact that antibiotics have beenadministered.

Most cases of clinical mastitis are treated without the benefit of bacteriologicalexamination of the milk before treatment is commenced. The treatment selectedis based on the severity of the mastitis, the history of the farm (including previousmilk culture results and responses to treatment), and the field experience of thefarmer and the prescribing veterinarian. In herd with clinical mastitis problems,milk samples should be submitted for culture to establish the farm profile ofmastitis-causing organisms and develop appropriate treatment and controlprotocols.

Treatment should always be administered according to the directions given onthe label and by the prescribing veterinarian. Recommended withholding periodsmust be observed for milk and meat.

Intramammary antibiotics

Intramammary treatment is practical and effective for cases where theinflammatory response does not occlude the teat canal or cistern.

Intramammary formulations should have the following qualities:• The formulation should cause minimal irritation to the udder.• The active ingredient must be effective against the bacteria.• The active ingredient must distribute well through the mammary gland

and persist in sufficient concentrations to effect a cure in localised areas ofinfection.

• The antibiotic should exhibit a low degree of binding to milk and udderproteins.

• The antibiotic should have a low degree of ionisation in the udder – in thisform they are better retained in the udder.

In general, a smaller amount of active ingredient is required to achieve therapeuticconcentrations when intramammary products are given compared to systemicdoses. However, the inflammatory process in affected glands may impededistribution of antibiotics.

Confidence – High

Antibiotics are legally restricted drugsthat must be prescribed by aveterinarian.


Although comparative efficacy data formany product formulations is not readilyavailable, there are appropriateantibiotics for the common pathogens.

Only use products registeredfor administration to foodproducing animals. Drugs suchas phenylbutazone andgentamicin MUST NOT beused. ✔

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Technote 4


A conflict exists between the duration of treatment (in many cases, longertreatment is associated with improved cure rates) and the desire to minimise theperiod over which milk must be withheld from the vat. All treatments havespecified minimum treatment courses that should be adhered to.

Dry Cow Treatment preparations should never be used in lactating cows.Inadvertent use of Dry Cow Treatment would require milk to be discarded forextended periods of time.

Systemic antibiotics

Acute mastitis cases may benefit from both intramammary and systemicantibiotics. Peracute cases often require systemic antibiotics and anti-inflammatory preparations, and possibly intravenous fluids. The prognosis forperacute cases in cows with severe clinical signs (as indicated by body temperature,dehydration, etc) is poor regardless of treatment.

Systemic antibiotics have the advantage that drug distribution is not impeded bylocal inflammatory reactions in the udder. However, to be effective, systemicantibiotic treatments must be absorbed from the injection site and pass from theblood into the udder. Their major difficulty is penetration of the “blood-milkbarrier”.

Drugs move across the blood-milk barrier by passive diffusion of the non-ionisedparts of the molecule according to the principle of osmosis. This barrier ispenetrated by the non-ionized, lipid soluble, non-protein-bound drug fractions.

Weak acids (e.g. penicillin G) are almost completely ionised in blood and havepoor tissue penetration. On the other hand, penethamate hydroiodide achievesconcentrations in the milk that are 5-10 times higher than other penicillin saltsdue to its basic and lipophilic properties. This treatment results in high levels ofpenicillin in the udder because it is hydrolysed as it crosses into milk liberatingactive benzyl penicillin.

Ampiclox LC

Cepravin LC

Lincocin Forte

Mastalone Blue

Orbenin LC

Special Formula 17900 Forte V

Intramammary products available for use in lactating cows in Australia (October 1999)

Product name Company Treatment course in Active ingredientsaffected quarters

Ampicillin 75 mg, Cloxacillin (sodiumsalt) 200 mgCefuroxamine sodium 250 mg

Lincomycin hydrochloride 200 mg,Neomycin sulphate 200 mg

Oxytetracycline 185 mg, Oleandomycin100 mg, Neomycin 100 mgCloxacillin (benzathine salt) 200 mg

Neomycin sulphate 150 mg, Novobiocin100 mg, Dihydrostreptomycin 100 mg

One syringe every 12 hours forthree treatmentsOne syringe every 12 hours in eachof three successive milkingsOne syringe, repeat at intervals notless than 12 hours, do not administermore than three consecutive dosesOne syringe, repeat daily forthree daysOne syringe every 48 hours forthree syringesOne plastet per quarter per dayrepeated at 24-hour intervals forthree days

Jurox

Schering-Plough

Pharmacia & Upjohn

Pfizer

Pfizer

Pharmacia & Upjohn

Technote 4.10 shows therecommended withholding periodsfor meat and milk for theseintramammary products.

Milk-to-plasma ratios of someantibiotics used to treatmastitis (Anderson 1989)

Antibiotic Milk-to-plasma ratio

Trimethoprim 3.7Lincomycin or Erythromycin 3.0Tylosin 2.0Tetracycline 0.7Streptomycin 0.5Ampicillin 0.25Sulphadiazine 0.21Penicillin G 0.15

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Allowing for antibiotic sensitivity patterns, antibiotics with high milk-to-plasmaratios are most suitable for systemic administration.

Recent clinical reports and studies suggest “that the combined systemic andintramammary antibiotic treatment may result in a slightly but significantly higherrate of bacteriological cure in the treatment of acute staphylococcal andstreptococcal mastitis” (Ziv 1997).

Published cure rates of antibiotics

Very little information is available to assess the efficacy and cost-effectivenessof treatment of clinical mastitis during lactation, and to compare products inAustralian conditions.

In a review of antibiotic treatment of clinical mastitis during lactation, Craven(1987) reported average cure rates for each antibiotic from scientific papers thatstated the number of quarters treated and had rigorous bacteriological assessment.From this data (see table below), it was not possible to draw firm conclusionsabout the relative effectiveness of different products given the wide range ofcure rates for similar antibiotics. There was a consistently greater bacteriologicalcure rate for treating Strep agalactiae infections than those due to Staph aureus,although cure rates are low for both organisms treated with neomycin.

Two recent clinical trials compared antibiotic products in clinical cases oncommercial farms in Australia or New Zealand:1.McDougall (1998) reported clinical cure rates of greater than 80% in 798

clinical quarters, predominantly due to Strep uberis, treated either with:• A course of high potency intramammary penicillin-dihydrostreptomycin –

containing 1 g of procaine penicillin and 500 mg of dihydrostreptomycin.This product is not available in Australia.

• Two subcutaneous injections of penethamate hydriodide in aqueous solu-tion of 10,000,000 IU followed by 5,000,000 IU 24 hours later. (This doseand method of administration is not recommended by the manufacturer ofpenethamate hydriodide in Australia. On the Australian label, the manufacturer specifies daily intramuscular injection of 5,000,000 IU for cattle.)

2.Wraight (1998) compared cefuroxime (Cepravin LC, Schering Plough) withcloxacillin (Orbenin LA, Pfizer Animal Health). Pathogenic bacteria wereisolated from 61% of pre-treatment samples, including Strep uberis (32%),Staph aureus (18%) and Escherichia coli (7%). There was no significantdifference between treatments with overall clinical cure rates of 82% in 416cases and bacteriological cures rates of 70%.

Efficacy of treatment with different antibiotics (Craven 1987)

Antibiotic Cure of Staph aureus Cure of Strep agalactiaeMean (%) Range (%) Reports (no.) Mean (%) Range (%) Reports (no.)

Penicillin 32 0 – 87 12 84 50 – 100 11Cloxacillin 41 21 – 84 14 92 40 – 100 8Neomycin 27 25 – 36 2 27 27 1Tetracycline 54 17 – 96 8Erythromycin 63 51 – 76 2Pen / Strep 39 21 – 78 5 91 91 1

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Technote 4


Specific mastitis treatments

The causative bacteria is usually not known at the time of treatment of individualcases so that the choice of treatment is based on the herd history, clinicaljudgement, and results of recent milk cultures.

Specific antibiotic treatment is indicated when cultures have been performedand the pathogen identity is suspected or confirmed. Some features of treatmentof clinical cases caused by common pathogens are listed below:

Strep agalactiae

• Strep agalactiae is highly sensitive to most of the commonly used antibiotics,and a high cure rate (>90%) can be expected using the correct antibiotic.

• Treatment stops shedding of Strep agalactiae by cows with clinical mastitis.• Treatment should be part of a total mastitis control program.

Staph aureus

• Bacteriological cure rate during lactation is low (about 30-60%) because Staphaureus causes micro-abscesses in the udder, survives inside cells, and someforms are resistant to commonly used antibiotics (e.g. strains with the enzymebeta-lactamase are resistant to penicillin).

• The best hope for successful treatment is in young cows with recent infections(of less than two weeks duration).

• Treatment of clinical mastitis may reduce Staph shedding, and result in milkreturning to clinical normality.

Strep uberis

• Experience shows some cases readily respond to treatment and others are quiterefractory to treatment. Recent research has found that field strains of Strep

uberis are able to invade and live in epithelial cells, which may partiallyexplain why infections are refractory to treatment (Keefe and Leslie 1997).

Escherichia coli

• Toxins produced by Escherichia coli cause the clinical signs of mastitis. Inmany cases, bacterial numbers are falling when clinical signs appear.

• Treatment aims to remove toxin by frequent stripping out and use of 30-60 IUoxytocin, and to minimise the effects of toxin by using anti-inflammatory agentsand possibly intravenous fluids.

• Systemic antibiotics are given when the cow is extremely ill or whenintramammary infusions are unlikely to diffuse through tissue because the udderis greatly swollen.

Technote 1 gives a list of actionsthat should be considered whenmanaging outbreaks of Strep uberisor Escherichia coli.

Technote 5 gives a list of actionsthat should be considered whenmanaging outbreaks of Strepagalactiae or Staph aureus.

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Supportive treatment

Injection with the milk ejection hormone oxytocin may help remove milk anddebris from hard, sore quarters. Oxytocin is a Prescription Animal Remedy andcan only be obtained through veterinarians.

There has been some discussion about treating mild clinical cases with oxytocinand frequent stripping rather than using antibiotics. In mild clinical cases ofcoliform mastitis, milk will usually return to normal within several milkings ifstripped frequently with 100 IU oxytocin (Guterbock et al 1993). (This dose ishigher than the Australian label recommendation of 30-60 IU.) In othercircumstances, oxytocin tends to alleviate clinical signs rather than effecting abacteriological cure. In a study of 40 herds, Hallberg et al (1994) found that itwas economically beneficial to use intramammary antibiotics to treat clinicalmastitis in lactating cows as this reduced the number of pathogens in the milkand increased the cure rate and number of quarters returning to normal milk.

Flunixin meglumine inhibits prostaglandin production and limits exudate at thesite of inflammation. In contrast with corticosteroids, flunixin does not inhibitwhite blood cell mobilisation at the infection site. Passage of flunixin from bloodto milk is poor, with levels in milk about 1% of those in blood. Nevertheless, ithas a useful systemic effect and helps reverse the clinical signs of shock in toxicforms of coliform or staphylococcal mastitis.

Salicylates, such as aspirin, may help reduce fever and inflammation but have alow potency and relatively short half-life. Although they are not registered foruse in cattle in Australia, some practitioners find them to be useful supportivetreatment (Whittem 1997a). In contrast, phenylbutazone has a long half-life (36-72 hours in cattle depending on the dose) but its action may be cumulative andtoxic. Phenylbutazone is NOT APPROPRIATE FOR USE IN CATTLE inAustralia. Large doses of dexamethasone (1-3 mg/kg) have been used to treatseptic shock in people with good results, but the treatment for cattle is costly andmay impair the natural defence mechanisms within the udder.

Large volumes of isotonic intravenous fluid (25-40 L) can markedly improve thechances of survival of cows suffering from acute toxic mastitis. In the early stagesof shock (for example, in cows that had a normal fluid status two hours earlier)small volumes of hypertonic saline have been used as an initial treatment to helprestore the circulatory blood volume.

Technote 4.6 discusses off-label useof animal treatments.

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Technote 4


4.5 Administer the treatment as recommended.

Administration of intramammary preparations

The nozzle of intramammary treatments can introduce bacteria into teats if theteat end is not properly disinfected. Fact Sheet B in the Countdown DownunderFarm Guidelines for Mastitis Control gives a detailed description of the correctway to administer intramammary treatments.

Ideally, antibiotics are given by partial insertion of short nozzle tubes just insidethe teat canal (1-2mm). This is unlikely to be achievable in cows that are not usedto having their teats touched, and may therefore not be appropriate for manyAustralian dairy herds. If an operator is not confident that short nozzle tubeswill be used correctly, long nozzle tubes should be used rather than risk damagingthe teat canal epithelium.

Confidence – High

There is strong evidence that udderinfusions can introduce pathogens unlessstrict attention is paid to sterile technique.

Research priority – Moderate

It may be beneficial to use systemicantibiotics rather than intramammarypreparations in targeted herds.

• Advisers are encouraged tocopy and distribute Fact SheetB in the CountdownDownunder Farm Guidelinesfor Mastitis Control to clients.

• It is necessary to emphasisethat udder cleanliness requiredfor good milking hygiene is notequivalent to, or stringentenough for, sterileintramammary infusions.

• Demonstration of teat endpreparation and intramammaryinfusion to staff whoadminister the treatmentsis worthwhile.

Administration of intramuscular antibiotics

Standards adopted by the Australian beef industry (CattleCare) to prevent carcasedowngrades and chemical residue problems are:• All injections are to be given into the muscles of the neck.• Injections are to be given in no more than 10 mL doses at any one site. For

example, when giving a 30 mL dose, inject 10 mL into each of three differentsites.

This is especially important for dairy cattle that may be culled within 12 monthsof treatment.

Use short nozzle tubes (right) when possible and insert just insideteat canal

✔

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G4.6 Use the full course of antibiotics (as specified on

the label).

The efficacy and treatment course for lactating cow formulations have beenestablished through extensive research for registration of the products(www.dpie.gov.au).

Only affected quarters of clinical mastitis cases should be treated. As a significantproportion of cows with clinical mastitis have more than one affected quarter, allquarters should be checked at each milking during the treatment course to enableearly detection and treatment of affected quarters.

Regardless of whether a clinically affected quarter shows rapid improvement, itis important to use the full course of antibiotic treatment specified by the productmanufacturer to reduce the likelihood of infection recurring because of inadequatetreatment, and to minimise the development of antibiotic resistant strains ofbacteria.

The development of antibiotic resistance

There is limited information on the rate that bacteria are developing resistance toantibiotics commonly used to treat infections in food-producing animals.

The likelihood of antibiotic resistance developing broadly depends on the:• prevalence of resistant bacteria in the animal population;• frequency of antibiotic use in the animal population; and• type of exposure to the antibiotics, e.g. short treatment courses of high doses

of antibiotic confer less selective pressure than long-term exposure to low dosesof antibiotic.

In addition to these factors, the rate of spread of antibiotic resistance within andbetween animal species will be influenced by the opportunity for contact betweenanimals and the host specificity of bacterial strains. It is therefore likely to varysignificantly with management systems, mix of enterprise types and geographiclocation.

One of the few published studies on the change in prevalence of resistant mastitisbacteria is in Finland, where Myllys et al (1998) reported an increase of 27% inthe proportion of Staph aureus strains resistant to at least one antibiotic (mostlydue to strains capable of producing beta-lactamase). There is currently nosubstantial data set that enables comparisons of this finding with what is happeningin the Australian dairy cattle population.

An expert advisory committee (JETACAR), considering the future managementof antibiotic use in food-producing animals, recommended that a mechanism formeasuring the rate of development of resistance in Australia be established. Asurveillance system to measure the incidence and prevalence of antibiotic-resistantbacteria and resistance genes in all areas of antibiotic use (including medical andveterinary applications) may be appropriate (JETACAR 1999).

Confidence – High

It is important to use the full course ofantibiotic treatment specified by theproduct manufacturer to reduce thelikelihood of infection recurring and tominimise the development of antibioticresistant strains of bacteria.


✔The JETACAR report can beviewed at the websitewww.health.gov.au/pubs/jetacar.htm

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Technote 4


Off-label use

Off-label use refers to an unregistered use of a product. This includes any deviationfrom the manufacturer’s recommendations, such as using a:• a different dose rate than stated on the label;• a different route of administration;• a different treatment interval; or• a drug for a different purpose to that stated on the label.

Off-label use can only be authorised by a consulting veterinarian and only wherestate legislation permits. It is done at the vet’s discretion, taking knowledge ofsafety and efficacy into account, and is usually restricted to situations where nosuitable registered product is available or where scientific evidence supportsoff-label use.

In food-producing animals, veterinarians prescribing off-label use of drugsbecome liable for setting appropriate withholding periods. These should be givento the client in writing. Wherever possible, the proposed treatment should beexplained to the owner and informed consent obtained before treatment is started.

4.7 Milk the quarter out fully at least every milking.

Section 4.4 describes supportive treatment for clinical mastitis cases.

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G4.8 Clearly mark treated cows.

All milking staff should be familiar with the system used on each farm to identifycows that have been given antibiotic treatment. The Food Quality Program (1999)gives examples of systems for temporary cow identification, all of which can bevery effective.

A separate identification system for marking cows that have received Dry CowTreatment allows for easy recognition if cows rejoin the herd in error, and canhelp relief milkers or casual staff avoid mistakes.

Confidence – High

Clearly marking treated cows decreasesthe risk of antibiotic residue violations.


Two examples of temporary cow identification (Food Quality Program 1999)

Comparison of methods of temporary identification by the New Zealand Ministry of Agriculture(Food Quality Program 1999)

Method Visibility Durability Ease of use

Velcro strip Excellent Good Easy to apply and remove

Insulation tape Excellent Good Easy to apply and cut offPlastic hock strap Excellent Very good Easy to apply and removeSpray paint (non-scourable) Variable Good Very simpleSpray paint (scourable) Variable Very poor Not suitableTailpaint Good Excellent Messy. Can paint over with new

colour after treatmentto avoid confusion

Paint stick/raddle Good Excellent Simple; use like a crayon

A cross differentiates the quarters – a

clear reminder from the rearUse red tape for front and blue for back

quarter

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Technote 4


4.9 Record all details.

Fact Sheet E of the Countdown Downunder Farm Guidelines for Mastitis Control

shows essential information to be recorded for each clinical case (including cowidentification, episode date, treatment details and withholding periods).

Advisers should encourage dairy farmers to keep permanent records of clinicalmastitis cases so they can manage individual cows and assess herd-level mastitiscontrol. For example, they can:• make decisions about how to dry-off cows (if selective Dry Cow Treatment is

being used);• make decisions about which cows to cull;• identify ‘suspicious’ cows (if clots are found on the filter or bulk milk cell

counts rise);• assess the number of mastitis cases and their response to treatment;• calculate the cost of clinical mastitis in their herd;• identify risk periods (e.g. stage of lactation) for clinical mastitis;• determine the main mastitis pathogen(s) in the herd; and• review the effectiveness of mastitis control and udder health on farms.

Herd improvement organisations have started providing services that can linkclinical case information with details of the cow’s age, production, individualcow cell counts (ICCC), previous clinical mastitis history, and Dry Cow Treatmenthistory (see example).

Example measures Whole herd Group comparisons within the herd Application

Lactation

numberPrevious Dry Cow

Treatment (yes/no)

Level of clinical mastitis in the herd ✔ ✔ ✔ Describe the level of clinical mastitis.(% or rate)Clinical cases by days after calving ✔ ✔ ✔ Identify risk periods. or in the dry period (% or rate)Episodes per clinical case (no.) ✔ ✔ Differentiate individual cow from herd

problem.Identify repeat cases for culling.

New versus chronic infections ✔ ✔ ✔ Assess effectiveness of Dry Cow(% or rate)* Treatment strategy.

Identify priority control measures.Volume of milk discarded (L) ✔ ✔ Establish cost of treatment.Duration of treatment (days) ✔ ✔ Establish cost of treatment.* Requires ICCC data.

Examples of measures used to assess clinical case management

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Data entry form for clinical cases of mastitis from the Maffra Herd Improvement Co-operative

Extract of a clinical case report from the Maffra Herd Improvement Co-operative

Clinical casesMonth of lactn 1 2 3 4 5 6 7 8 9 10Cases/100 cows 8 2 1 1 1 1 0 0 0 0Target 5 2 2 2 2 2 2 2 2 2

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Technote 4


4.10 Observe withholding times for milk and meat.

Withholding periods (WHP) refer to the minimum period of time that must elapseafter the last administration of a drug before an animal or its products are soldfor human consumption.

Pharmaceutical companies provide recommended withholding periods for theirproducts. Antibiotic residues in milk or meat will not exceed the relevantAustralian Maximum Residue Limit if treatments are used according to the labeldirections and milk or meat are withheld for the specified withholding periods.

Recommended withholding periods are based on trials that specify the:• class of livestock, e.g. lactating cows;• dose rate, e.g. milligrams of drug per kilogram liveweight of animal;• dose interval, e.g. given once daily;• duration of treatment course;• route of administration, e.g. intramammary infusion or intramuscular

injection;• use of drugs within their expiry date;• use of drugs stored in accordance with label directions; and• pattern of use for which they are registered, e.g. individual animal treatments.

Any deviation from the registration specifications described above may lead tochanges in the withholding periods for a product. Such changes are unlikely tobe linear (e.g. doubling the dose cannot be extrapolated to a simple doubling ofthe required withholding periods) (Whittem 1997b).

When giving systemic treatments for mastitis it is important to calculate thecorrect dose, as withholding periods for milk and meat change markedly whendrugs are used at higher dose rates than specified on the label. Weights can bemeasured on scales or by using girth measurements and height sticks as a guide.

Recommended withholding periods for milk and meat after Lactating Cow Treatment (October 1999)

Product Withholding period

After last infusion After last feed of treated milk

Milk Cow meat (days) Calf meat (days)

Ampiclox LC 72 hours 30* 30*Cepravin LC 72 hours 7 Must not be fed to

(6 milkings) bobby calvesLincocin Forte 96 hours 30 30Mastalone Blue 7 days 30* 30*Orbenin LC 96 hours 30 30*Special Formula 72 hours 30 3017900 Forte V

Figures with an asterisk are not from material approved by the National Registration Authority, but provided by the pharmaceutical companies as consistent with

NRA-approved withholding periods for other products. Contact the manufacturer or a veterinarian for further information.

Technote 4.4 describes the activeingredients and treatment course forthese intramammary products.

Technote 3.1 gives comparableinformation for Dry Cow Treatments.

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GMilk should be withheld from thevat if there is any suspicion thatthey contain antibiotic residue.Samples can be submittedfor antibiotic testing to helpresolve problems.

High dose rates constitute an ‘off-label’ dosage and, for any prescription drug,can only be considered with written permission from a veterinarian. They are acommon cause of antibiotic violations.

For registration purposes, the National Regulatory Authority requires withholdingperiods to be based on the product sold for consumption. Consequently,withholding periods for intramammary antibiotics for lactating cows refer tocows and calves sold for meat or vats of milk.

In Australia, failure to observe withholding periods after treatment is the mostsignificant cause of residue non-compliance (Nicholls et al 1994). In dairy cattle,antibiotic violations are often associated with:• inadvertent use of Dry Cow Treatment in lactating cows (note that Dry Cow

Treatment is registered only for use immediately after a cow’s last milking fora lactation);

• failing to identify treated cows;• failing to record treatment dates;• cows treated with Dry Cow Treatment at drying-off mistakenly rejoining the

milking herd;• ‘off-label’ drug use and• cows treated with Dry Cow Treatment calving before expiry of the Minimum

Dry Period.

Antibiotic residue tests

Traces of antibiotic in milk may cause allergic reactions in people and inhibitsome starter cultures used in cheese production. National and internationalregulations stipulate the maximum levels of antibiotics that may be present inmilk and these thresholds are often extremely low (Victorian Dairy IndustryAuthority 1999). Dairy companies perform regular screening tests to detectinhibitory substances in the vat milk that they collect. The dairy industry alsoconducts an independent survey of bulk raw milk for antibiotic (and other)residues, called the Australian Milk Residue Analysis. This service provides acredible monitoring system that helps the Australian Quarantine InspectionService to sign off on European Union exports.

Any factory will conduct tests for farmers if there are concerns that antibioticsmay have contaminated the vat. The tests include microbial inhibition tests suchas the widely used Delvotest SP (DSM Food Specialists) and Disc assay (DifcoLaboratories), or assays such as Lak Teck (Idetek Inc.), Penzyme (SmithKlineBeecham Animal Health), CITE (IDEXX Corp.) or Charm II (Charm SciencesInc.). The tests should be performed by operators experienced in using the kits toobtain valid results.

✔

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Technote 4


These screening tests have been designed and validated for use on vat milk andare likely to give false positive test results if they are applied to individual milksamples. For example, non-specific inhibitory substances present in the milk offreshly calved cows or clinical mastitis cases are likely to give a positiveDelvotest SP test result (Cullor et al 1993). Inhibitory substances and antibioticresidue detected in an individual milk sample may not be excessive once it isdiluted with clean milk in the vat. However, testing individual milk samples withfactory screening tests provides a cheap and conservative approach to ensuringcontaminated milk does not go into the vat.

Vat screening tests are relatively non-specific and vary considerably in their abilityto detect all antibiotic families. A more sophisticated and expensive method forquantifying and identifying the type of antibiotic present is High Pressure LiquidChromotagraphy (HPLC). Although this is more suited for testing milk samplesfrom individual cows, the cost (about $100) is likely to be prohibitive in normalcircumstances.

4.12 Make a particular effort to minimise spread of

bacteria from infected cows to other cows.

Technote 8 describes good hygiene during milking.

4.11 Discard milk from all quarters of cows that receive

treatment.

Even when a single quarter has been treated with intramammary antibiotic, it ispossible that some antibiotic will be absorbed into the bloodstream and pass intothe milk of normal quarters. The risk of antibiotic contamination is too great toinclude milk from treated cows in the vat.

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G4.13 Consult your veterinarian for advice about the

following options if a clinical quarter fails to

respond by the end of a full course of treatment

(as listed on the label).

The reasons why a clinical quarter may fail to respond to treatment need to beconsidered when giving advice to clients. These may include:

• Inappropriate choice of drug.

Drugs which do not have the spectrum of activity required to combatinfections in a particular herd will be ineffective.The pharmacological properties of some drugs make them inappropriate foruse in mastitis therapy. For example, although some drugs are effective invitro they may be ineffective in vivo if they are unable to cross to the site ofthe infection.

• Physical obstruction preventing drugs reaching the site of infection.

Examples are accumulations of inflammatory cells and hyperplasia ofalveolar epithelium.Infections, such as Staph aureus, can lead to fibrosis and formation of micro-abscesses within the udder. Many antibiotics are unable to crossthese barriers in sufficient concentration to reach the minimal inhibitoryconcentrations required at the site of infection.

• Attributes of the bacteria.

Staph aureus bacteria, sensitive in vitro to the antibiotic used, may gain refugewithin the acid phagolysosomes of macrophages and polymorphonucleurneutrophils with the udder. Antibiotic penetration of cells may be poor andeven if they gain access to the cell they may not distribute to thephagolysosomes.Other organism-related reasons for treatment failure include infections thatare resistant to useable antibiotics (e.g. Pseudomonas, mycoplasma, yeasts,etc.) and the emergence of L-forms (‘naked’ acapsular forms that resistbeta-lactam antibiotics).

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Technote 4


Options when there is no response to treatment

Options that can be considered when a clinical quarter fails to respond to a fullcourse of treatment are discussed below.

• Repeating the treatment but treating for an extended time with the antibiotic.Oxytocin should be used at milking to assist as much milk removal as possi-ble in conjunction with repeated antibiotic treatments. Note that repeatedtreatments may extend the required withholding periods.

• Trying a different antibiotic treatment.

This will be effective if the infection is more susceptible to the newantibiotic or if the physical properties of the antibiotic allow it to reach theinfection site more effectively.The longer a case of clinical mastitis persists, the greater the degree offibrosis and abscessation that may occur, and the less likely the quarter is torespond to antibacterial treatment. Some cases just do not respond totreatment.

• Drying-off the infected quarter if it is not hot and swollen. The cow should be in good general health apart from the infected quarter.A simple method of drying-off a quarter is to stop milking the quarter, aslong as it is monitored to ensure that it does not develop into an acute case ofmastitis. It is important that these quarters are permanently identified toprevent accidental attachment of cups to these teats at the time of milking.Dry Cow Treatment must not be used in a quarter when the other quartersare continuing to be milked. Dry Cow Treatments are not registered for usein lactating cows. Some antibiotic will be absorbed into the bloodstream andpassed out in the milk from the normal quarters, so there is an unacceptablerisk of antibiotic contamination of the vat. At the end of lactation it is notappropriate to use Dry Cow Treatment in a quarter that has been dried offduring lactation because intramammary Dry Cow Treatments will not beabsorbed in dry quarters. Advisers may consider using injectable antibioticsat the end of lactation in these cows.Stubborn cases of mastitis may be treated by preventing the quarter fromproducing further milk permanently while retaining the cow in the herdwith three viable quarters. An alternative approach is to infuse an irritantchemical solution (5% copper sulphate, or a solution of chlorhexidinediacetate as per Boddie and Nickerson 1994) into the affected quarter toproduce a chemical mastitis that causes it to permanently dry-off. From theanimal welfare perspective, the short-term inflammation caused is prefer-able to the long-term inflammation and other potential problems associatedwith chronic mastitis. It is notable that most farmers do not reportany significant drop in production of the other three quarters during thechemical cauterisation treatment. It is not acceptable, for animal welfarereasons, to remove a teat by use of an elastrator ring or other means (unlessthe teat is gangrenous as a result of the mastitis infection).

• If a milk sample was collectedand frozen before the initialtreatment, it can be cultured todetermine the causal bacteriaand their antibiotic resistance.

• Pathogens introduced at thetime of treatment (due to poortechnique when givingintramammary infusions)will only be identified byresampling the quarter. ✔

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• Drying-off the affected cow.Drying-off cows with quarters that fail to respond to treatment removes asource of infection to other cows in the milking herd. These cows may betreated with Dry Cow Treatment and the affected quarter closely monitored –if the quarter becomes hot and swollen, or the cow becomes systemically ill,treatment with lactating cow product in the infected quarter may need to bereinitiated.

• Culling chronically infected cows from the herd.Culling chronically infected cows is an important component of any mastitiscontrol program. The recommended withholding period for meat must beobserved if the cow has been treated with antibiotics.

Using chemical solutions to permanently dry-off quarters:

• The cow should be in good general health.

• The quarter is milked out thoroughly with hand stripping and oxytocininjections.

• The quarter is infused with 20 mL of 5% copper sulphate solution and notmilked for seven more days. After infusion, it exhibits a large degree ofinflammation with associated heat, swelling and mild to moderate pain.The pain and heat generally subside within the initial week posttreatment and the swelling over the next weeks.

• On the eighth day, it is hand-stripped; if there is any sign of milk, theprocedure is repeated. If there is only serous fluids, the quarter iscleared of as much fluid as possible and not milked any further. ✔

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Technote 4


Key papers

Anderson KL. Therapy for acute coliform mastitis. The Compendium, Food Animal 1989; 11:1125-1133.

Boddie RL, Nickerson SC. Evaluation of chlorhexidine diacetate for permanently drying off chronicmastitic quarters. Agri Practice 1994;15(1):12–16.

Claxton PD, Ryan D. Bovine mastitis. In: Corner LA, Bagust TE, editors. Australian StandardDiagnostic Techniques for Animal Diseases, CSIRO for the Standing Committee on Agriculture andResource Management, East Melbourne, 1993.

Craven N. Efficacy and financial value of antibiotic treatment of bovine clinical mastitis duringlactation – a review. Brit Vet J 1987;143:410–422.

Cullor JS, Van Eenennaam A, Gardner I et al. Problems associated with cowside and bulk tank antibioticresidue testing. In: Proceedings of the 32nd National Mastitis Council Annual Meeting, KansasCity, Missouri, 1993:133–143.

Donovan GA, Risco CA, Shearer JK. Assessment of the mammary system. In: Wilson JH editor.Veterinary Clinics of North America Food Animal Practice, Physical examination, WB Saunders,Sydney, 1992;8:361-372.

Food Quality Program. Cow identification Dairy First Fact Sheet 2-4. Guidelines for a dairy farmHACCP system: reference manual. Department of Industry, Science and Tourism and Dairy Researchand Development Corporation, February 1999.

Gunn AA, Malmo J, Anderson GA, Caple IW. The effects of clinical production of dairy cows in herds fedpasture. In: Proceedings of the XX World Association of Buiatrics Congress, Sydney, 1998:921-926.

Gunn AA, Malmo J, Anderson GA, Caple IW. The incidence of bacteria associated with clinicalmastitis in the Macalister irrigation district. In: Proceedings of the Australian Association of CattleVeterinarians, Hobart, 1999:197-206.

Guterbock WM, Van Eenennaam AL, Anderson RJ, et al. Efficacy of intramammary antibiotictherapy for treatment of clinical mastitis caused by environmental pathogens. J Dairy Sci1993;76:3437-3444.

Hallberg JW, Henke CL, Miller CC. Intramammary antibiotic therapy: to treat or not to treat? Effectsof antibiotic therapy on clinical mastitis. In: Proceedings of the 33rd National Mastitis CouncilAnnual Meeting, Orlando, Florida, 1994:28-39.

JETACAR. The use of antibiotics in food-producing animals: antibiotic-resistant bacteria in animalsand humans. Report of the Joint Expert Technical Advisory Committee on Antibiotic Resistance,Commonwealth of Australia, Canberra, 1999.

Keefe G, Leslie K. Therapy protocols for environmental streptococcal mastitis. In: Proceedings of thesymposium on udder health management for environmental streptococci, Ontario Veterinary College,Canada, 1997: 75-86.

Luedecke LO, Forster TL, Williams K, Hillers JK. Effect of freezing and storage at –20oC on survivalof mastitis pathogens. J Dairy Sci 1972;55:417-418.

McDougall S. Treatment of clinical mastitis in New Zealand dairy cows. In: Proceedings of the XXWorld Association of Buiatrics Congress, Sydney, 1998:303–307.

Murdough PA, Deitz KE, Pankey JW. Effects of freezing on the viability of nine pathogens fromquarters with subclinical mastitis. J Dairy Sci 1996;79:334-336.

Myllys V, Asplund K, Brofeldt E et al. Bovine mastitis in Finland in 1988 and 1995 – changes inprevalence and antimicrobial resistance. Acta Vet Scand 1998; 39:119-126.

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