Milk

Let-Down

Got Milk?

How does milk get from the cow to the table?

The Milk WayAlveoli membentuk air susudi dalam rongga-rongga susudari bahan baku yg disupai

oleh darah

“Ductule” dari masing-masing alveoli

mengalirkan air susu kesaluran-saluran kecil

air susu

Ke saluran-saluran Besar air susu

Gland cistern

Teat cistern Dari “streak canal ke

Ujung puting

AND NOWYOU’VE

GOTMILK!!

Milk is stored here between milking’s.

Necessity of Milk Letdown• It has been documented repeatedly that a full and complete milk letdown is

dependent on the dairy cow receiving proper stimulation at milking time. Whenthis stimulation fails to occur or when the timing and sequence of the stepsinvolved is inappropriate, the end result is frequently sub-optimal.

• The dairy cow produces and stores a great percentage of the milk producedbetween milkings in the alveolar region of the gland where it is produced, ratherthan in the cisterns of the udders and teats. Consequently proper pre-milkingstimulation is critical in order to allow this milk to be released so that it can beharvested. We breed and manage dairy cows to produce huge volumes of milk.Regardless, until letdown is initiated, the majority of this milk remains in thealveolar tissue where it is produced.

• We know that stimulating the nerve endings in the teats and teat ends, when doneproperly, is the ideal way to cause the release of oxytocin from the brain. It then istransported by the blood stream to the udder where it acts to cause milk in thealveolar spaces to be released to the udder and teat cisterns. This is thefundamental basis of milk letdown.

• Many of today’s dairy farms are very large and operate up to 24 hours/day. Theequipment in use is expensive, sophisticated and durable. Owners expect, afterinvesting large amounts of money in fixed assets, that such assets be fully utilizedand generate a reasonable pay back. It is a business and there is nothing wrongwith the logic.

Milk Ejection Reflex

• The milk ejection reflex actually is aneuroendocrine reflex. The reflex has anafferent pathway (neural) and an efferentpathway (hormonal, blood-borne).

Afferent Pathway• The greatest amount of innervation in the mammary gland is in the

teats, where there are pressure sensitive receptors in the dermis.

• Mechanical stimulation of the teats activates pressure sensitivereceptors in the dermis where the pressure is transformed into nerveimpulses that travel via the spinothalamic nerve tract to the brain. Thesenerves synapse in the paraventricular nucleus and in the supraopticnucleus in the hypothalamus.

• When the cell bodies of the oxytocin-containing neurons are stimulatedby these impulses originating in the teat, an action potential movesdown the oxytocin-containing neurons from the cell body in thehypothalamus down the axon to the neuron ending in the posteriorpituitary. This causes release of oxytocin and neurophysin into the blood.The efferent pathway starts at this point.

Efferent Pathway

• The efferent pathway begins with the release of oxytocininto the blood. The oxytocin then travels to themammary gland via the blood, binds to oxytocinreceptors on the myoepithelial cells, causing themyoepithelial cells to contract, and resulting in increasedintra-lumenal (intramammary) pressure and ejection ofmilk from the alveolar lumen.

• Oxytocin receptors are associated with the myoepithelialcells, not the smooth muscle of the mammary gland. Inmice these receptors increase through-out gestation, butare fairly constant through lactation. (see Soloff, 1982, J.Dairy Sci. 65:326)

Although this seems straight-forward, the biological mechanisms involved are complex. [See J. Dairy Sci. 1983 66:2251]

For example:

• Manual stimulation of the teat or nipple is not required for oxytocin release ormilk ejection. Oxytocin can be released by conditioned visual and auditorycues, such as the sights and sounds of the milking parlor (occurs in ~38% ofcows), resulting in milk letdown.

• Oxytocin is not always measurably elevated in blood during milk letdown. Milkyields of mammary glands transplanted to the neck region in goats is nearnormal despite having eliminated oxytocin release due to direct udderstimulation and innervation.

• No measurable increase in oxytocin in the blood after stimulation is seen in38% of goats and 32% of cows studied.

Oxytocin and Milk Ejection

• Oxytocin is a 9 amino acid long peptide. The amino acid structure of oxytocin is:

Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly

• It has a molecular mass of 1007 daltons. Oxytocin has a disulfide bond between the two cysteines. Reduction of the disulfide bond inactivates oxytocin. One IU (international Unit) is approximately 2 micrograms of pure peptide.

• Oxytocin is syntheized in the hypothalamus in specific nuclei, the paraventricularnucleus and the supraoptic nucleus in the hypothalamus. [A cluster of nerve cells in thebrain is often called a nucleus. This is different from the nucleus of a single cell.]Neurons in these hypothalamic nuclei synthesize the oxytocin precursor and package itinto vesicles. Oxytocin is initially synthesized as a large molecular weight precursorwhich also consists of the oxytocin-carrier peptide neurophysin. The precursor isproteolytically cleaved in the neuron in the oxytocin-containing vesicle to yield oxytocinbound to neurophysin. The oxytocin-neurophysin complex is the intracellular storageform of oxytocin.

Myoepithelial cells surrounding a mammary alveolus

Pre-Milking Stimulation

Oxytocin Surge• The oxytocin concentration in the blood normally is increased within 1 to 2 minutes after

udder stimulation, but the amount released is declining during milking.

Why is pre-stimulation of the cow needed before milking?

• Hygiene - for prevention of mastitis and for maximizing milk quality.

• Milk ejection - [see J. Dairy Sci. 1980 63:800] In this study they compared milking aftermanual stimulation (washing the teats) vs. nonstimulated (milkers were put straight onthe gland with no pre-washing or other stimulation). The manual stimulation resulted inshorter machine-on times (higher milking efficiency) and higher peak and average milkflow rates.

• Milk flow rate - [see J. Dairy Sci. 1985 68:1813] In this study, average milk flow rateincreased with increasing duration of udder stimulation (30, 60, 120 sec.) and milkingmachine-on time decreased.

Other Roles of Oxytocin

• Injection of oxytocin into the ventricles of the cerebellum in rats inducesmaternal behavior.

• Oxytocin has insulin-like activity and it may be lipogenic. The mother is rapidlylosing a great deal of lipid when milk is removed.

• Both oxytocin and prolactin are implicated in osmoregulation. The mother israpidly losing a great deal of water when milk is removed.

• Oxytocin-containing neurons from the paraventricular and supraoptic nuclei goto other brain regions which are involved in autonomic regulation (such ascardiovascular effects). In these cases, oxytocin is acting as a neurotransmitter.

• Oxytocin may be directly or indirectly involved in prolactin release duringproestrus in the rat.

Milk Removal

Milk removal is required for maintenance of lactation!!!

• Milk removal from the lactating mammary gland is the majorfactor in maintaining milk secretion.

• Milk accumulation in the gland causes an increase in intramammary pressure, which reduces blood flow to the tissue.

• Higher frequency of milking in ruminants results in greater activities of milk synthesizing enzymes per cell in lactating tissue.

Milking or Nursing Frequency

• The frequency at which milk is removed from the mammary gland by the suckling offspring varies substantially among species. For example:

Nursing frequency may be: Species

continuous kangaroo (joey)

or at intervals of:

.5 hr whale, dolphin

1 hr pig

4-6 hr cow

1X/day rabbit

1X/2 days tree shrew

1X/week Northern fur seal

Milking Frequency in Dairy Cattle

• In the case of dairy cattle, management considerations determine howoften cows are milked each day. In most dairy cattle managementschemes, cows are milked twice daily or three times daily.

Milking Interval

• For 2X/day milking of dairy cattle, the optimuminterval is 12 hr; milk accumulation has notsignificantly lowered the milk secretion rate, butby ~14 hr there is a decline in secretion rate.

• Compared with a 12 and 12 hr milking interval ina 24 hr period, 9 and15 hr interval results in1.8% less milk yield, while a 8 and 16 hr intervalresults in 3.4% less milk.

Mammary Nerves & Stress

Norepinephrine and epinephrine can inhibit oxytocin-induced contraction of myoepithelial cells.

Stressful stimuli will inhibit milk ejection. This occurs via epinephrine or norepinephrine derived from the adrenal gland or the sympathetic nerves by the following mechanisms :

• Norepinephrine reduces myoepithelial cell contractial response to oxytocin;this is a direct inhibition at the myoepithelial cell level.

• Norepinephrine decreases mammary blood flow (amount of oxytocin to thegland); this is an inhibition at the mammary tissue level.

• Norepinephrine reduces oxytocin release from the pituitary; this is an indirecteffect mediated by inhibition of oxytocin release at the hypothalamic level.

12 golden rules for milkingBefore milking

1. Monitor

udder health

regularly

Review regularly all udder health and milk quality information

provided by the dairy plant, official testing organizations, veterinary

clinics and on farm testing using the DeLaval cell counter (DCC) or

the California Mastitis Test (CMT).

Develop benchmarks for each cow and herd to assist in monitoring

changes that may occur.

2. Milking

order

Regardless of housing system or herd size, milk first calf heifers, fresh

cows next and then the main herd.

Milk sick cows last and then wash and sanitize the milking system.

3. Foremilk cows

Remove 2-3 squirts of foremilk and examine it. In tie stall and

parlour facilities use a strip cup. Wash off the parlor floor before the

next group of cows enters.

Foremilking provides a powerful signal to initiate milk let-down and it

provides an opportunity to detect and prevent abnormal milk from

entering the tank.

4. Clean teats and

teat ends

Mastitis control and producing high quality milk requires that cows

have clean, dry teats when units are attached. Clean each teat and teat

end using approved materials. Wipe each teat dry using single service

paper or cloth towels, one per cow. If cloth towels are used be certain

to effectively launder and dry them before reusing.

Never start the milking procedure with cleaning of teats! The result is that germs growing in the teat canal

can be moved further up into the udder. Always start with foremilking before cleaning of teats!

During milking5. Check

Milking

System

Select a vacuum level and pulsation system appropriate for

the dairy farm and have it installed according to DeLaval

specifications.

Always check the vacuum level at the start of each milking.

6. Attach

milking

cluster at

appropriate

time

Within 60-90 seconds of all teat preparation procedures,

milking units need to be attached.

Minimize air entries during cluster attachment.

Adjust milking cluster so that it is properly balanced front to

back, side to side with no twisting.

7. Avoid

over-

milking

Overmilking is considered a primary cause of teat end

hyperkeratosis. When the udder has been emptied

satisfactorily, the milking unit needs to be removed. This can

be detected by manual observation or, for systems with

ACR’s, allowing flow sensors to detect low flow and direct

the automatic removal of the cluster. Flow controlled milking

systems provide a visual indication when low flow has been

attained.

8. Ensure

proper

removal of

cluster

When milking is completed vacuum to the cluster can be

shut-off manually or automatically. Allow claw vacuum to

decline completely before removing the unit. DO NOT

squeeze the udder and pull down on milking units as this

may lead to air entry around the liner mouthpiece, this has

been implicated in new cases of mastitis.

After milking

9. Sanitize

teats after

each milking

As soon as possible after the unit is removed sanitize each teat with an approved

post milking teat dip or spray. This is the single most effective procedure to

prevent the cow to cow spread of contagious mastitis organisms.

10. Clean

milking

equipment

immediately

after milking

Clean off the external surfaces of the milking system.

After each use, either manually or automatically rinse and clean all system

components using appropriate products at the proper temperature. Allow the

system to drain dry.

Where required, sanitize the system prior to the next milking using approved

sanitizers at the proper dilution.

11. Properly

cool milk

Check cooling temperatures to be certain the proper temperatures are being

reached during and after each milking.

Proper refrigeration temperatures greatly slow or stop the growth of most

bacteria.

12. Monitor

milk quality

milking

equipment,

and milking

performance

data regularly

Review all milk quality, milk composition, and milking center performance

information regularly and compare it to historical data.

Replace liners and rubber goods according to recommendations. Old rubber

goods become cracked and porous and this influences milking performance and

increases the risk of soil and bacterial build-ups. Such problems may lead to

increased milking times and higher bacteria counts.

Have the total milking system serviced regularly according to the DeLaval’s

recommendations.

http://www.delaval.com/Dairy_Knowledge/12_golden_rules.htm

Human Milk Let-Down

Milk let-down may occur in these situations:

♥ when you think about your baby

♥ hear your or another baby cry

♥ when it is your scheduled nursing time

♥ when you are sexually stimulated or during

orgasm.

42

SFCC: Figure 14.14

Interference with Let-Down A variety of factors may interfere with let-down:

♥ Emotions: embarrassment, anger, irritation, fear or resentment

♥ Fatigue

♥ Inadequate sucking (Improper positioning or insufficient amount of time baby is actively nursing.

♥ Stress

♥ Negative remarks from relatives or friends

♥ Fear of pain in your breasts or uterus (i.e. sore nipples or afterbirth pains)

♥ Breast engorgement in the first few days

Suggestions for Creating a Supportive

Nursing Environment

♥ Find a peaceful atmosphere for nursing. Before beginning the feeding, unplug thephone, turn on relaxing music, and take four or five deep abdominal breaths.

♥ If breastfeeding in public inhibits you, insist on your privacy and/or drape a lightcover over your baby and your shoulder to cover up.

♥ Interact with friends and breastfeeding professionals who are supportive ofbreastfeeding. Do not let well-meaning friends and relatives who have differentattitudes discourage you. Restrict visitors until you are comfortable.

♥ Be around other nursing mothers. Attend a postpartum exercise class and/orpostpartum support group.

♥ Be sure your baby is positioned properly and allow adequate suckling.