Lactation

Question 1

describe prenatal mammogenesis (4)

Answer 1

1. mammary ridge (thickening of epidermal tissue) forms the primary mammary bud as epidermal tissue bulge inward into the dermis (mesenchyme)
2. secondary mammary bud develops as the primary bud starts branching further into the dermis
3. canalization occurs when ducts start to form and myoepithelial cells begin to line the terminis of the glands
4. at birth, the mammary glands have developed as lactiferous glands that empty into ducts that empty via a teat or nipple

Question 2

describe post natal mammary gland growth (7)

Answer 2

1. is endocrine mediated
2. between birth-puberty growth is isometric
3. between puberty and pregnancy growth is allometric
4. duct and alveolar system refines with each estrous cycle
5. ducts branch and increase in diameter under the influence of estradiol
6. progesterone influences alveoli formation (the functional secretory unit)
7. prolactin and GnRH aid estradiol in more rapid duct development

Question 3

describe final mammary gland development during pregnancy

Answer 3

during the last trimester the terminal alveoli grow into lobules that make up close to 90% of the cellular mass by parturition

Question 4

what is the first-milk? describe its immune role

Answer 4

colostrum! high in antibodies (IgG) for initial immune protection, as animals with epitheliochorial and endothelialchorial cannot have IgG cross the placenta

Question 5

describe the anatomy of teats in camels, mares, sows, cow ewe goats, dog and cat, and primates and elephants

Answer 5

camel: 2 canals per teat, inguinal location

mares: 2 ducts per teat, inguinal

sows: 2 ducts per teat, across entire ventrum

cow, ewe, goat: 1 canal/cistern per teat, inguinal location

dogs and cats: 5-6 ducts per teat, 10 mammary glands on entire ventrum (don’t even bother treating intramammary)

primates and elephants: 8-10 ducts per nipple/teat

in mares and other animals with more than 1 duct per teat, keep in mind when treating mastitis!! treat both ducts

Question 6

describe the physiology of lactation (5)

Answer 6

1. estrogen: stimulates mammary duct development
2. progesterone: stimulates lobuloalveolar growth and inhibits lactogenesis
3. trigger for lactogenesis is a drop in P4 and an increase in prolactin late in gestation
4. onset of lactation is controlled by the HPA, ovaries, and placenta
5. galactopoeisis (lactation maintenance) is influence by ovarian and adrenal steroids, prolactin, oxytocin, GH, insulin and a shit to of other factors

Question 7

describe lactogenesis

Answer 7

milk is produced in mammary alveolar cells and has 3 components

1. proteins: synthesized in rough ER and transported to golgi, packaged into vacuoles that pinch off and fuse with the alveolar cell membrane and are released into the alveolar lumen (major proteins are casein, lactoferrin, a-lactalbumin, and IgA)
2. fat: delivered to mammary glands via serum chylomicrons from GI tract
3. triglycerides are hydrolyzed at the capillary level and glycerol and FFAs enter alveoli by passive diffusion

Question 8

what is the principle osmotically active compound in milk?

Answer 8

lactose! determines the amount of water; high lactose = high water

Question 9

what happens to milk prior to suckling?

Answer 9

pools in alveolar lumen and smaller ducts draining to lumen; experiences strong resistance to flow in smaller ducts

Question 10

what is milk secretion?

Answer 10

synthesis and movement from alveolar cell into alveolar lumen

Question 11

what is milk ejection?

Answer 11

active transfer of milk from alveoli and alveolar ducts into mammary ducts, cisterns, and teats/nipples by contractile myoepithelial cells

Question 12

describe the neuroendocrine reflex that governs milk ejection (4)

Answer 12

1. sensory neurons in udder detect suckling
2. afferent nerves transmit these signals to the paraventricular nuclei of the hypothalamus
3. the hypothalamus stimulates posterior pituitary to release oxytocin into the bloodstream, which stimulates myoepithelial cells surrounding the alveoli to contract
4. milk is ejected into the ductal system

Question 13

describe plasma prolactin in the mare (3)

Answer 13

1. increases in the last week of gestation and stays high for the first 1-2 months postpartum
2. at max concentrations 2-3 days postpartum to stimulate max milk production until baby can suckle and stimulate on its own
3. produced by lactotrophs in anterior pituitary, regulated by hypothalamic secretion of dopamine

Question 14

describe colostrum composition (3)

Answer 14

1. antibodies from maternal blood concentrate in milk during last 2 weeks of gestation
2. is also a source of nutrients, vitamins, complement, lactoferrin
3. can be affected by premature lactation and lead to failure of passive transfer

Question 15

describe colostrum absorption (4)

Answer 15

1. enterocytes in small intestine non-selectively absorb colostral IgG by pinocytosis
2. enterocytes engulf droplets from intestinal lumen, transfer it by small vacuoles, and empty into lymphatic vessels that travel through portal system to bloodstream
3. best absorption:
   foal: 0-8 hrs post partum
   calf: 0-12hrs
   dog: 0-12hrs
4. all colostrum absorption stops by 24hrs old because those specialized enterocytes are replaced by cells that can’t pinocytosis

Question 16

how is colostrum quality measure?

Answer 16

IgG increases fluid density, so measure density, or radial immuno diffusion via Brix

Question 17

describe mare udder development

Answer 17

1. plaque udder edema up to 2 months pre partum
2. udder filling 2-3 weeks before or within 12 hrs for maiden mare
3. waxing!!: dried colostrum on tip of teas within 24-48 hours of birth, pretty reliable sign

Question 18

describe equine mammary electrolytes

Answer 18

1. sodium high early gestation
2. then switch to low salt, high calcium approx 48 hours pre foal, so calcium a good indicator of foaling

Question 19

describe milk pH as indicator of foaling

Answer 19

1. early mammary secretions pH approx 8
2. colostrum pH approx 6.4
3. secretions more acidic = baby close

Question 20

is there a downside to monitoring milk pH and calcium to determine foaling?

Answer 20

yah, placental pathology can cause abnormal pH and electrolyte profiles

Question 21

when is peak lactation in the mare?

Answer 21

1-2 months post partum, 10-12kg per day

Question 22

describe canine mammary structure difference from everyone else

Answer 22

lacteal ducts do not merge into the teat cistern and instead open directly into the teat via 7-20 distinct canals

Question 23

describe canine pre and psot partum lactation

Answer 23

1. can lactate a few days prior to whelping
2. can delay lactation 24-48 hrs postpartum = bad for baby
3. peak milk yield is 3 weeks postpartum and declines by 3 months or earlier if weaned and can produce up to 6 percent of body weight in milk per day

Question 24

describe mammary gland involution (3)

Answer 24

1. neonate suckling less frequently increases pressure in the gland
2. pressure atrophy of secretory cells occurs and if sudden can stop milk synthesis in just a few days
3. immune invasion of lymphocytes and macrophages occurs to help prevent infection

Question 25

describe induction of lactation in mares (6)

Answer 25

1. to use non-foaling mares as nurse mares
2. prime with P4 and estradiol for 7-14 days
3. administer prostaglandin and estradiol to simulate foaling
4. administer a dopamine antagonist to stimulate milk production for 14 days
5. on day 7 begin milking the mare 5 times a day to stimulate milk production
6. initiate fetal adoption on day 10