Lactation

The Udder

Milk Production

• After birth, milk production peaks and then gradually decreases. Birth of a calf stimulates hormone production which causes milk letdown

• After approximately 305 days, the cow should “go dry”, or stop producing milk. – If the cow is not re-bred, she will not produce any

more milk. – An approximate 60-day drying off period is vital to

milk production because it allows time for the udder to heal.

Milk Production

• If the cow is not milked during her 305-day lactation period, she will also “go dry”.– Milking, either by hand or mechanically, stimulates

milk production over the lactation period

Colostrum

• Colostrum is the first milk to come from a cow after birth and contains a high concentration of antibodies.

• The calf’s intestines at birth are very porous, which allows it to absorb the antibodies from the milk. – The intestines begin to “close up” from 24-48 hours after

birth, so it is imperative that the calf suckles within the first 24 hours of life.

• The calf must ingest the colostrum in the first 24 hours because colostrum gives the calf immunity against disease

Hormones

• Prolactin is involved in the development and differentiation of mammary gland

• Oxytocin causes the muscles to contract and squeeze the milk into the milk ducts and toward the teat

• Epinephrine signals the let down and stopping of milk flow

How does milk travel from udder to milker?

• Prolactin stimulates the alveoli cells to produce milk.

• The milk drains into the lumen of the alveoli.• The clusters of alveoli, called lobules, contain

ducts that drain into larger ducts. These larger ducts drain into the gland cistern.

• The milk is stored in the gland cistern.• The sphincter muscle prevents the milk from

leaking into the teat.

Trends in dairy production

• In nature, animals only produce enough milk for their offspring. Over time, we have selected high producing animals that have come to produce excess amounts of milk

• Changes have come about due to improvements in genetics, feeding, and environmental conditions

• We now have fewer cows with more production, fewer farms with more cows, and more Grade A milk

Why 3rd world countries don’t have dairy cows

• They are not adapted to the hotter, drier conditions• They require more maintenance than may be

available• They might not survive limited grazing/feeds that

may be available• The countries have few to no transportation

systems.• Households will generally have one or two hardy

animals to produce milk for the family– Goats

Other dairy animals

• Goats• Sheep– Goats and sheep can survive on less feed than

cows. – They can also utilize browse better than cattle.– A ewe’s milk has twice the fat and 40% more

protein than cow’s milk.• Camels• Horses

Let down

• The hormone oxytocin is released by the pituitary gland into the bloodstream when the udder is stimulated.

• Oxytocin causes the alveoli to “squeeze” and release the milk.

• Oxytocin release can be caused by: washing the udder prior to milking, suckling of the calf, or other pleasant stimuli.

• If an animal becomes frightened or upset, a hormone called epinephrine is released that inhibits milk letdown.