The Purpose of the Milking Routine

The Babcock Institute © 2004 Debora A. Costa and Douglas J. Reinemann

The Babcock InstituteUniversity of Wisconsin

Dairy UpdatesMilking and Milk Quality No. 407 Author: Debora A. Costa and Dr. Douglas J. Reinemann2

Introduction12

There are three primary objectives of the pre-milking routine: Sanitation, Abnormal milk/Clinical mastitis detection, Stimulation.

These objectives must be achieved in a waythat is friendly to the cow. Recent research hasemphasized the importance of the human-cowinteraction in the success of the milk letdownresponse and the milking process.

Producers of high-quality milk know that aconsistent method of pre-milking udder hygieneand the uniform attachment of properlyfunctioning milking machines are important.The objective of milking management is toensure that teatcups are applied to calm cowswith visibly clean, well-stimulated teats; milk israpidly and efficiently harvested; and milkingunits are removed when milking is completed.Results show that applying a post milkingsanitizer is effective in reducing mastitisinfections.

The seven habits of highly effective milkingroutines identified by Ruegg, et al. [32] aresummarized as:1. Cows are calm and clean before milking.

1 Paper presented at the 43rd National Mastitis Council,February 1-4, 2004, Charlotte, North Carolina.

2 Debora Costa is a Graduate Research Assistant in theDepartment of Dairy Science; and Dr. Douglas J.Reinemann is a Professor in the Departments ofBiological Systems Engineering, Dairy Science and theUW Milking Research and Instruction Lab at theUniversity of Wisconsin-Madison.

2. Cows are grouped by infection status (ormilked in a way to avoid transfer ofpathogens by the milking machine).

3. Consistent pre-milking cow prep is used.4. Teats are clean and dry before attaching

milking units.5. Milking units are attached properly (at the

correct time, without excessive airadmission, and adjusted to hang evenly onall four quarters).

6. Milking units are promptly and properlyremoved at the end of the milking.

7. Cows are managed post-milking(Application of post-milking sanitizer withcows kept standing toallow teat canals toclose).

SanitationThe pathogen concentra-

tion in or near theenvironment of the teatorifice appears to have THEdominant influence on rate ofnew mastitis infection [25].It is clear from both fieldstudies and controlledresearch that the majority ofnew mastitis infections occurwhen teat ends are exposedto pathogens in the housingarea. It is estimated that 80 to94 percent of new infectionsoccur in the animal housingarea. Sanitation of the

The Purpose of theMilking Routine

In thisDairy Update

1Introduction

1Sanitation

2Abnormal Milk

and ClinicalMastitis

Detection2

Stimulation3

ComparativePhysiology ofMilk Removal

5Stimulation

Requirements forMilk Removal inCrossbred Cows

6References

The Purpose of the Milking Routine and Comparative Physiology of Milk Removal in Bovine Species

2 Dairy Updates 2004

housing area thus has the overriding influenceon the mastitis infection rate.

Sanitation of teat ends at milking helps toremove manure, mud, and pathogens thataccumulate at the teat end before milking.Sanitation also reduces the number of pathogensthat are deposited on liners and can betransferred to other cows. Removing pathogensfrom the teat skin two or three times per daymay also reduce the risk of infection betweenmilkings. The milking process also plays a rolein removing pathogens that have becometrapped in the keratin lining of the teat canal andthus reduce the risk of mastitis infection. Thesepoints are illustrated by the high rate of mastitisinfections that occur during the dry period whenteats are not cleaned regularly and the keratinlining of the teat canal is not removed andreplaced. The mechanism of bacteria transportinto the teat sinus during the dry period has not,as yet, been fully explained.

Abnormal Milk and ClinicalMastitis Detection

There is considerable debate in the dairycommunity on the need to practice fore-stripping. While there is no hard evidenceavailable, dairy professionals estimate that fore-stripping is not uniformly practiced either inEurope, where it is required by law, or in therest of the world.

When teat sanitation requirements are met itis also likely that the tactile stimulation isadequate to produce the milk letdown responsein the majority of cows. Perhaps the mostimportant reason to fore-strip cows is to detectabnormal milk and other signs of clinicalmastitis. One way to reduce the transfer ofcontagious organisms from cow to cow is toestablish a milking order in which infected cowsare milked last (or with a designated milkingunit). Infected cows must be identified in orderto implement this practice. Identifying clinicallyinfected cows and diverting their milk from thebulk tank may also be a critical element inmaintaining bulk tank somatic cell counts in adesirable range on some farms. Examination of

udders and fore-milk is the quickest way toidentify infected cows and may be the onlymethod of detection on many farms.

Another benefit of requesting that milkersfore-strip cows is to improve the odds that majordebris will be removed from teats and that sometactile stimulation will occur as part of the pre-milking preparation process.

StimulationThe milking machine is a remarkably

effective stimulation device. The tactilestimulation provided by the machine iscomparable to calf suckling or hand stimulation.However, the milking machine also appliesphysiological stress to the teat skin and tissues.The effects of these physiological stressesbecome increasingly undesirable as the machineis applied to cows for longer periods because ofincreased milk yield in high-producing cows,over-milking, or a combination of these.Applying the milking machine to an udder thathas already undergone the milk ejection reflexcan reduce these undesirable effects.

It appears that 10 to 20 seconds of tactilestimulation is sufficient to elicit oxytocinsecretion in high-producing cows [32]. The lagtime from start of tactile teat stimulation untilfull milk ejection ranges from 60 to 120 secondsand depends on the degree of udder filling,which, in turn, depends on the interval betweenmilkings and the stage of lactation [6]. This lagbetween oxytocin release and milk ejection isaccounted for by the time required to transportthe hormone from the brain to the udder and forthe alveoli to fully contract. Oxytocin has half-life of approximately 1.5 to two minutes [27].These relationships have given rise torecommendations for optimal prep-lag times[30, 31].

According to these time relationships theoptimal application of manual stimulationwould include 10 to 20 seconds of tactilestimulation at the point of first contact with thecow, followed by unit attachment 60 to 120seconds after this first contact. Tactilestimulation applied immediately before milking


Milking and Milk Quality No. 407 3

unit attachment is not likely to producesignificant added benefit for stimulation. Tomake the best use of the manual stimulation thefirst contact with the cow should includeapplication of pre-dip and manipulation of theteats to:1. Remove debris and2. Fore-strip to detect abnormal milk.

Some cows may not express milk during thisfore-stripping process, but the attempt willensure that tactile stimulation has occurred onthese animals that have a higher stimulationrequirement, and it is more likely thatobservation of the condition of each quarter forredness and inflammation will occur.

The following review of literature on thecomparative physiology of milk removal willhelp to illuminate these points as well as providethe basis for adjusting milking routines forcrossbred cows and other species.

Comparative Physiology ofMilk Removal

Milk is stored within two compartments ofthe mammary gland: the cistern (including teatand gland cistern, and large milk ducts) andalveoli (small milk ducts and alveoli). Thecisternal milk can be easily removed bysuckling, hand, or machine milking without anyprevious stimulation. However, the alveolarmilk can only be removed if milk ejectionoccurrs. Tactile stimulus on the mammarygland activates a neuroendocrine mechanismthat releases oxytocin into the blood stream.Oxytocin causes myoepithelial cells thatsurround the alveoli to contract and force themilk expulsion into the cisternal compartment[7]. There are wide differences among speciesin the physiology of milk ejection reflex [15].

The milk ejection reflex is instinctive and isnot under the conscious control of the animal.Suckling, hand milking and machine milkingcause sufficient tactile stimulation to inducemilk ejection, although the literature reportsdifferences in the intensity of stimulation causedby suckling and milking machine.

For instance, it is shown that suckling haseither stronger [5, 21, 33], weaker [2] or similar[13, 26, 36] effect in stimulating the milk let-down compared with cows machine-milkedwithout the presence of the calf. Nevertheless,most authors [2, 13, 36] agree that there is ahigher oxytocin release in response to sucklingas compared with milking in the presence of thecalf. In comparison with hand milking, machinemilking resulted in a smaller release of oxytocin[17]. The extents of hand stimulus effects arevariable, possibly arising from inter-breedvariation in the response to stimuli [39].

Good pre-milking stimulation improved themilking performance of cows (higher peak andaverage milk flow rates and decreased milkingtime) compared with cows that received nostimulation [18]. The work of Mayer, et al. [23]indicated that oxytocin secretion remainedabove the threshold required for milk ejectionthroughout lactation. However, Bruckmaier andBlum [7] explained that, because of the reducedvolume of milk stored in the udder at the end oflactation, full milk ejection usually takes longerto occur and pre-milking stimulation is moreimportant during this period.

Feedback inhibitor of lactation (FIL) is amilk-borne protein synthesized by secretorycells, which has an inhibitory action on the samecells, limiting further milk secretion [41]. FIL isonly active in the alveoli, in contact with thesecretory cells, and its effect is concentrationdependent. The excess of residual milk due toincomplete milk ejection increases theconcentration of FIL in the alveoli anddecreases milk secretion. The distribution ofmilk between cisternal and alveolarcompartment will influence the degree offeedback inhibition in different species [20].

A common mechanism of milk ejectionseems to apply to the majority of speciesstudied. However, there are species differencesin the need for degree of oxytocin release atmilking [1]. For instance, two animal modelsare used to explain the different patterns of themilk ejection reflex. In the rabbit model, initialsuckling by the litter induces the release of asingle pulse of 20-50 mµ oxytocin and milk



removal is completed in two to five minutes. Inthe rat model, multiple pulses of 0.5 to 1.0 mµof oxytocin are released at intervals of 5 to 15minutes throughout suckling periods of 30 to 60minutes. The sow’s milk ejection is similar tothe rabbit model, whereas human andruminants’ milk ejection patterns are moresimilar to the rat model [12].

There are large differences in the proportionof total milk stored within the cistern amongruminant dairy species. The size of the cisternalso varies with milking interval [38].Specialized dairy cows store less than 30percent of the total milk yield volume in thecistern with a normal milking interval [4]. Incontrast, the cisternal fraction accounts for up to75 percent in dairy goats [22], and in sheep itranges more than 50 percent for dairy breeds[24] to less than 30 percent for meat breeds [9]

It is argued that milk ejection may not beessential for adequate milk removal in animalsthat store most of the milk in the gland cisterns[1, 12]. Oxytocin release in goats occursimmediately after the start of stimulation,causing a tendency for immediate decrease inmilk flow rate after unit attachment (unlikecows) [8]. Marnet and McKusick [22] foundthat oxytocin-mediated milk ejection is ofprimary importance in small ruminants toextract milk that is rich in fat. Although thecisternal compartment stores most of the milkproduced in small ruminants, the alveoli retainthe majority of the milk fat secreted, which canbe only efficiently removed when milk ejectionoccurs [24].

Buffalo cows store almost 95 percent of theirmilk in the alveolar compartment with the smallcisternal capacity most prominent in the teatarea. As a result, pre-milking stimulation isextremely important for milk ejection andmilking units should only be attached afterinitiating the milk ejection response [37]. Milkejection in buffalos also requires about twominutes of tactile stimulation and calf sucklingis often used for this purpose when hand-milking. The practice of using calves is not ascommon in herds where buffalo cows aremachine milked in parlors [34].

In camels, the presence of the calf isconsidered imperative for milk letdown, andhand massaging is also used to enhance thisresponse. Milk letdown in this species is easilynoticeable after a short period of suckling (1.5minutes) when the teats suddenly swell,becoming much larger than before. Milkingneeds to be performed soon after the teat-swelling, since the duration of the milk letdownresponse is very short, approximately 1.5minutes. Because of this fact, some authorsassume that camels do not have mammarycisterns. Camels are able to refill their udder inabout 30 minutes after complete milking byhand, to suckle their calves [42].

The pig possesses numerous mammaryglands without cisterns. Ellendorff and Poulain[14] reported that the nursing intervals occurredabout every 45 minutes, and lasted for 8 to 40seconds. A study of the milk ejection reflex inthe sow found that the whole litter had to besuckling in order to elicit the milk ejectionresponse, which occurred between two and fourminutes from the onset of the period of initialmassage of the udders [14]. Today, it is knownthat the milk ejection can be induced by rubbingthe front teats in some sows [19].

Another difference in the milk ejection reflexamong mammalian species is the influence ofexteroceptive stimuli (evoked by sight, smell,and/or sound from the nursing young or themilking place). In lactating rats, rabbits andguinea pigs, oxytocin is released only inresponse to tactile stimulation (“unconditioned”type of milk ejection reflex). On the other hand,ewes released oxytocin under conditions ofexteroceptive and tactile stimulation [16].There are some indications that exteroceptivestimuli usually turn into “conditioned” milkejection reflexes, especially when a regularmilking routine is adopted [18].

Interestingly, audio stimuli—in the form ofcalf calls—were not clearly shown to causeoxytocin release and affect the rate of milkejection in Holstein cows [29]. Similarly,Mayer, et al. [2] did not find any evidenceindicating that conditioned oxytocin release istriggered by audio-visual stimuli. In contrast,



Hurley [19] argues that tactile stimulation of theteat is not essential for oxytocin release andsubsequent milk ejection. Hurley’s data [19]indicate that about 38 percent of cows releaseoxytocin by conditioned visual and auditorycues, such as the sights and sounds of themilking parlor.

Fuchs, et al. [16] suggested that species inwhich the tactile stimulus is the only means totrigger the oxytocin response is linked to little orno mammary cistern, whereas those who releaseoxytocin at the sight and smell of their offspringhave such compartments.

Stimulation Requirements forMilk Removal in CrossbredCows

Bos taurus cows were more intensivelyselected for milk production than Bos indicuscows. In high-yielding dairy breeds, suckling, anatural stimulation for milk letdown, wassuccessfully replaced by hand stimulation.Perhaps one of the consequences of geneticselection of Bos taurus cows was an alterationin the regulation of milk ejection [36]. Sincethese cows were also selected for rapid milkingand ease of milking, it is suggested that theyprobably acquired a reduced dependence on themilk ejection reflex [1]. In contrast, artificialmilk removal through hands of unfamiliarpeople or milking machines is still not wellaccepted in some Bos indicus cows. The entiremechanism responsible for the inhibition ofmilk ejection in cows remains unclear [36].

The release of oxytocin in the milk ejectionreflex can be disturbed at the central level or theperipheral level of the nervous system underpractical conditions. Milking conditions such assuckling by an alien calf, calf removal beforemilking, milking a cow in the presence of itsown calf, or unknown milking place can affectthe regulation of milk ejection [36].

In contrast, with specialized European dairybreeds, in which milk production in the secondlactation is usually higher than the first, it wasdemonstrated that crossbred cows had a linear

reduction in milk yield in successive lactations.The lactation length was also graduallyshortened [3]. The authors suggested that thiscould be attributed to the “special behavior” ofcrossbred cows being milked without theircalves.

Four milking strategies were applied to cowscontaining 50 to 75 percent of Holstein genetics:1. Milking without the presence of the calf,2. Suckling the calf before milking and

separating the calf immediately afterwards,3. Tying the calf near the head of the cow

throughout milking, and4. Suckling the calf before milking and tying

the calf near the head of the cow throughoutmilking.

This experiment showed that an equivalentamount of saleable milk was obtained fromcows stimulated by suckling before milking orby the simple presence of their calves duringmilking. The yield for these treatments wasgreater than the amount of saleable milk fromthe group of cows milked without calves. Theauthors also found that a considerable amount ofmilk is suckled after milking, even in cows thatwere stimulated by calves during milking, thusindicating that milk ejection at milking is notcomplete [10].

A similar experiment applied three treatmentsto Zebu crossbred cows:1. Calves allowed to suckle for a short time

before milking and then tethered to the neckof the cow during milking,

2. No suckling before milking but calves weretethered to the neck of the cow (physicalcontact), and

3. Cows were able to see, smell and hear theircalves without making physical contact.

Each cow-calf pair rotated through thetreatments three times. Suckling plus physicalcontact led to the highest milk yield (P<0.001).Physical contact by itself also enhanced milkproduction, but to a lesser degree [28].

Cows that have the genetic potential for milkproduction but receive a poor diet may havetheir udders incompletely filled, which couldlead to a weaker milk ejection response. The



major feed resource for dual-purpose cattleraised in the tropics is grasses with a varieddegree of supplementation, which is sometimesonly provided during the dry season. There issome evidence indicating that an udder that isnot well filled may take extra time foroccurrence of milk ejection. It is suggested thatthe delayed milk ejection response at low levelsof udder fill is probably a consequence ofdelayed response of the oxytocin in themammary gland. In order to force milk out ofan incompletely filled alveolus, it is necessarythat more myoepithelial contraction occur,which requires more time, resulting in a delayedejection of milk to the cisternal compartment[6].

Wellnitz et al. [40] found that cows ofEuropean breeds at different production levels(> 45 kg/d and 25 to 30 kg/d) but similar stagesof lactation, in which their udders are filled tothe same level, had comparable patterns of milk

ejection. It may not be possible to extrapolatethese results to cows with Bos indicus geneticsbecause their udder fill, at the same stage oflactation, may not be comparable to Bos tauruscows.

A study by Costa [11] found no evidence thatcalf suckling increased milk flow rates (whichwould indicate enhanced stimulation) butsuckling did appear to be associated with alower somatic cell count in Zebu-Holstein cowsin Brazil. The elimination of calf sucklingduring milking simplifies the milking routineand results in significant labor savings.Nevertheless, suckling may still berecommended for those cows that have anaggressive behavior during milking. Geneticselection for temperament may have alreadyreduced the benefits of using calves duringmilking and may continue to reduce or eliminatethese benefits in the future.

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3. Alvarez, F.J., G. Saucedo, A. Arriaga, and T.R. Preston. 1980. Effect on milk production and calf performance ofmilking cross bred European/Zebu cattle in the absence or presence of the calf, and of rearing their calves artificially.Trop. Anim. Prod. 5: 25-37.

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9. Caja, G., X. Such, J. Ruberte, A. Carretero, and M. Navarro. 1999. The use of ultrasonography in the study ofmammary gland cisterns during lactation in sheep. In: Proceedings of the Sixth International Symposium on the Milkingof Small Ruminants: Milking and milk production of dairy sheep and goats. p91-93.

10. Combellas, J., M. Tesorero, and L. Gabaldón. 2003. Effect of calf stimulation during milking on milk yield and fatcontent of Bos indicus x Bos taurus cows. Livest. Prod. Sci. 79: 227-232.

11. Costa, D.A. 2003. Surveys of milking characteristics and milk quality of Brazilian crossbred dairy cows. MastersThesis, University of Wisconsin-Madison.



12. Cross, B.A. 1977. Comparative physiology of milk removal. In: Comparative Aspects of Lactation. Edited byMalcolm Peaker. Symp. Zool. Soc. Lond. 41: 193-210.

13. de Passillé, A.M., J. Rushen, and P.G. Marnet. 1997. Effects of nursing a calf on milk ejection and milk yield duringmilking. J. Dairy Sci. 80, Suppl. 1, p203.

14. Ellendorff, F. and D. Poulain. 1984. A means to assess nursing efficiency in the pig: the study of the milk ejectionreflex. Ann. Rech. Vét. 15: 271-274.

15. Ellendorff, F., M.L. Forsling, and D. Poulain. 1982. The milk ejection reflex in the pig. J. Physiol. 333: 577-594.

16. Fuchs, A-R., J. Ayromlooi, and A.B. Rasmussen. 1987. Oxytocin response to conditioned and nonconditioned stimuliin lactating ewes. Biol. Reprod. 37: 301-305.

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19. Hurley, W.L. 2002. Lactation Biology ANSCI 308 - University of Illinois (lesson: Milk Ejection). Web-site:http://classes.aces.uiuc.edu/AnSci308.

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37. Thomas, C.S., K. Svennersten-Sjaunja, M.R. Bhosrekar, and R.M. Bruckmaier. 2003. Mammary cisternal size,cisternal milk and milk ejection in Murrah buffaloes. J. Dairy Res. (in press).

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40. Wellnitz, O., R.M. Bruckmaier, and J.W. Blum. 1999. Milk ejection and milk removal of single quarters in highyielding dairy cows. Milchwissenschaft 54: 303-306.

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Permission to print this Babcock Institute Publication was given by the authorsDebora A. Costa and Douglas J. Reinemann,who retain the copyright for this material.

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The Purpose of the Milking Routine