What are the milk secreting cells?
What cells are important for the milk ejection reflex?
What are the functions of alveolus?
-To remove nutrients from the blood. -To transform the nutrients to milk -To discharge the milk into duct system
Describe the structure of the alveolus
Billions of alveroli into lobule, group of lobules into a lobe..
lobule= 10-100 alveoli
lobe= group of lobules
What are mammogenesis, lactogenesis and galactopoieses?
Mammogenesis- Mammary gland development (anatomy)
Lactogenesis- initiation of milk syntheisis (secretion)
Galactopoiesis- milk syntheisis (maintenance)-secretion
In relation to mammogenesis: What are isometric and allometric growth?
Isometric growth= mammary glands are growing at same rate as the rest of the body tissues (first 2-3 months of life).
Allometric growth= mammary glands are growing at 2-3 times the growth of the rest of the body.
Describe allometric growth phase and after allometric growth phase
Allowmetric growth phase: At 2-3 months after birth to onset of puberty. Rapid growth of fat pad, duct system, connective tissue. Some alveoli formed.
After allometric growth phase: 2-3 kg mammary weight (up to 20 kg in first lactation). 10-20% epithelial cells (40-50%). 40-50% connective tissue (40%). 30-40% adipose (very little).
(proportions during lactation)
What happens if you overfeed during the allometric growth phase?
Leads to larger mammary glands, more adipose tissue and less secretory tissue.
Higher growth rates but decrease milk production in the future, up to 30%.
Mammogenesis- puberty to conception. What happens in the second isometric growth phase?
Ovarian follicles produce estrogen- udder cistern, ducts.
CL produces progresterone- alveroli
Estrogen, progesterone act 'in concert' - ovariectomy (removal of ovaries)
GH, thyroid hormones, adrenal hormones (cortisol) also are important for "full" udder development. Limited effect if adrenal or pituitary glands are removed.
mammogenesis will continue under the infulence of estrogen and progesterone.
Duct system develops during the first 3 months of pregnancy.
Alveoli develop mostly towards the last trimester.
Discuss lactogenesis- around parturition
Secretory cells of the alveoli start to produce milk.
Surge in prolactin, decreases in progesterone around parturition is the singal to start lactation.
Lactose synthase: Alpha-lactalbumin synthesis is induced by hormonal change. Galactosyl transferase: alpha-lactalbumin complex (1:1). Transfers galactose to glucose (beta 1,4 linkage)
Lactose is osmoregulatory- determines milk volume. (stimulates the uptake of water into the lumen)
Galactopoiesis: what are the three important hormones?
Discuss the most important one.
Prolactin: Higher levels on long photoperiod (16h light and 8 h dark). Major galatopoietic hormone in non-ruminants. Suckling stimulates prolactin release- increases milk production (removal of milk is very important for milk production)
Growth hormone: Major galactopoetic hormone in ruminants.
Insulin-like growth factor (IGF)-1
When does peak milk yield occur?
6-8 weeks into milking
What does involution mean?
The gradual, but irreversible regression of the gland. Reduction in the number, and metabolic activity of the active alveoli.
What are some ways that we manipulate the lactation curve?
Discuss drying off. When is occurs? What it does?
45-60 days prior to next calving. Reduces the amount of concentrate fed, stop milking. Mammary gland involution and renewal of alveoli. 20-25% decrease in the next MY if there is no dry period!!!
What is the main componenent of milk?
In most species the major componenent is water.
Solid-not-fat = protein, lactose, mineral, vitamins
What is the major osmo-regulator of milk?
Lactose is the major osmoregulator
What is the most important E source of milk?
FFA, MG, DG, TG
Milk fat forms globules. Homogenization produces very small globules which do not seperate (rise)
What are the proteins in milk?
Just be famillair with. Major component are the caseins
What are some factors affecting milk composition?
Colosturm vs mature milk.
Milk protein, fat percent
What does gut closure have to do with colostrum?
Suckling helps to close the gut.
Ability to recieve intact immunoglobin declines with gut closure.
Discuss immunoglobulins and lactoferrin in terms of calf health
Immunoglobulins: provide passive immunity prior to gut closure. Intestinal lumen protection for remainder of lactation (but IgGs are much lower from this point on)
A rich source of nutrients
Lactoferrin: Binds iron- helps wiht immune support, imporves digestion and absorption. Makes Fe unavailable to bacteria.
What are the growth factors present in milk?
Insulin, GH, IGF-1, IGF-11 ect. (responsible for development of GIT)
Formula milk will not contain the important growth factors for the calf, result in less developed GIT.
In milk composition, what is always constant
Milk lactose content is constant (4.8-5 %)
What milk composition component is hard to change in dietary manipulation?
Milk fat content
What type of diet leads to milk-fat depression?
HIgh grain, low fiber diets. Diets that create acidosis. Diets high in polyunsaturated FA's.
Other factors to milk dat depression: Genetics, season (less miok fat on hot summer heat), milking technique.
More grain= more milk yield. But high grain diets result in decrease in milk fat content.
What are some factors affecting milk yield?
Feed composition and intake: 30kg milk/d = 4kg dry matter in milk. INcreased nutirent density- energy, protein. Increased feed frequency ( will promote more feed intake, more nutirents for milk production_.
Milking frequency: 15-20% increase in MY when swithcing from 2x to 3x milk. Removal of feedback inhibitor of. lactation; reduced mammary pressure; stimulation of prolactin, GH release. (milking stimulates the production of more milk).
Litter size: Level of demand by offspring affects yield. Increased litter size increases milk yield. Neural stimulation of prolactin secretion in non-ruminants. Unused glands involuute and do not recover.
Hormones: Bovine somatotropin (BST) or GH
What is the role of oxytocin in milk let down?
Oxytocin causes contraction of myoepithelial cells (to squeeze the milk out of the lumen).
Milk released from alveoli into duct system to teat (which is the drainage system for the mammary gland
What is the conditioned reflex?
When might an injection be required and of what?
Conditioned reflex is the response of a cow to specific stimuli, that leads to milk letdown. ex) enter the milk parlor, sound of the machines, udder prep.
Oxytocin injections may be required to help a heifer who doesn't have a conditioned reflex yet. Only one or two milkings do this, or could interupt the regular hormone.
What is the important of pre-milking stimulation?
Pre-milking stimulation results in the oxtocin release.
Maximal effect of oxytocin during the first 2-5 min of milk let-down
[oxytocin] decline rapidly after 6-8 min