Lactation Physiology

Question 1

what are the stages of mammary development

Answer 1

1. fetal mammary chain and bud development
2. peri-pubertal spurt
3. peri and postpartum differentiation
4. involution

Question 2

does fetal mammary chain/bud development depend on hormones

Answer 2

NO - growth is isometric

males: testosterone induces regression of mammary chain

Question 3

does the pubertal spurt of mammary development depend on hormones

Answer 3

YES - requires high estradiol, cortisol, and GH

Question 4

what hormones drive peri and postpartum mammary development

Answer 4

estradiol, cortisol, GH, progesterone, and prolactin

BOTH progesterone and prolactin must be present to completely develop ducts and alveoli

Question 5

involution

Answer 5

“drying off period” that allows the mammary tissue to regress when not lactating

Question 6

does the mammary tissue completely regress during involution

Answer 6

NO - mammary tissue will accrue with each lactation

Question 7

in the last trimester, does the concentration of progesterone and prolactin increase

Answer 7

NO - the increased response comes from an increase in RECEPTOR number

Question 8

effect of progesterone on mammary tissue and milk production

Answer 8

• promotes mammary tissue growth
• inhibits milk production

need HIGH progesterone to develop mammary glands, but LOW progesterone to initiate milk production

Question 9

effect of prolactin on mammary tissue and milk production

Answer 9

stimulates milk production in mammary tissue

Question 10

steps of lactogenesis

Answer 10

1. a-lactalbumin and galactosyl transferase combine to form lactose synthase enzyme
2. lactose synthase converts glucose and galactose into lactose
3. lactose creates an osmotic gradient within the mammary gland to draw water in and produce milk

Question 11

what is the rate limiting factor of lactogenesis

Answer 11

a-lactalbumin

Question 12

effect of prolactin + cortisol

Answer 12

promotes a-lactalbumin expression in mammary epithelial cells to increase lactose synthase activity and lactogenesis

Question 13

does cortisol alone stimulate a-lactalbumin

Answer 13

NO - requires prolactin

cortisol + prolactin results in a synergistic effect to amplify a-lactalbumin expression

Question 14

effect of progesterone on a-lactalbumin

Answer 14

inhibits a-lactalbumin

Question 15

hormonal changes that occur at parturition

Answer 15

• prolactin: increases to program lactation curve then decreases after parturition; NOT needed throughout lactation
• progesterone: withdrawal at parturition initiates lactation
• bST: stimulates milk production to extend the lactation curve

Question 16

bST

Answer 16

bovine somato-mammotropin; growth hormone in dairy cattle used to extend length and yield of lactation

Question 17

colostrum

Answer 17

first milk after parturition that is abundant in immunoglobulins for antibody transfer to neonate

required in species with epitheliochorial placentas

Question 18

what is the window of neonatal colostrum absorption

Answer 18

within 24-36 hours BUT ideally want to administer within 1 hour

earlier ingestion = more efficient absorption while the gut is open

Question 19

what hormone promotes colostrum absorption in neonates

Answer 19

prepartum fetal cortisol increase

premature babies = no fetal cortisol = poor colostrum absorption

Question 20

milk ejection reflex

Answer 20

neuroendocrine reflex

• suckling induces OT release from posterior pituitary
• OT stimulates contraction of myoepithelial cells in mammary glands
• results in milk let down

Question 21

does oxytocin stimulate lactogenesis

Answer 21

NO

Question 22

drying off

Answer 22

increase intra-mammary pressure induces mammary epithelial atrophy leading to involution of the mammary gland over weeks between lactations

essential for regaining maximum milk production in next lactation cycle

Question 23

lactational anestrus

Answer 23

suckling inhibits the reactivation of the hypothalamic pituitary axis to prevent cycling while the dam is lactating

occurs in NON SEASONAL animals only

Question 24

do horses, sheep, or dairy cattle exhibit lactational anestrus

Answer 24

NO
- horses: have “foal heats” and can gestate again 2-3 weeks postpartum
- sheep: enter seasonal anestrus after lambing
- dairy cattle: reovulate 1-2 weeks postpartum due to production setting of milking (NOT nursing young - only get milked a couple times a day)

Question 25

effect of lactation on weight/metabolism

Answer 25

lactation has a HIGH metabolic demand (up to 3x basal metabolic intake)

causes significant weight loss
- more weight lost = longer time required to return to cyclicity

Question 26

agalactia

Answer 26

no mammary gland development resulting in no milk production

common in cows and mares grazing on fescue grass w/ prolactin inhibiting toxins

treat with oxytocin or surrogate nurse for neonate

Question 27

milk fever

Answer 27

hypocalcemia that occurs at parturition leading to periparturient paresis

low Ca prevents Ach release at neuromuscular junctions

occurs in COWS
- treat with IV calcium

Question 28

eclampsia

Answer 28

hypocalcemia that occurs at peak lactation leading to tetany/tremors

occurs in DOGS
- treat with IV and SQ calcium and remove suckling pups

Question 29

ketosis

Answer 29

drain on the nutrient reserve of the cow during peak lactation (4-8 weeks postpartum) causing the cow to be in negative energy balance –> ketosis