Control of lactation

Question 1

When is colostrum produced?

Answer 1

secretion accumulated at the end of last pregnancy and secretion formed during first 24 h after parturition.

Question 2

What does colostrum contain?

Answer 2

Contains more proteins, fat, minerals and vitamins than regular milk. However lactose concentration is lower.
Proteins: transfer of IgG, IgM, IgA from blood to milk.

Question 3

What is the function of colostrum?

Answer 3

Supplies the newborn with immunoprotection.

Very important in equidae and bovidae.

Question 4

Why is colostrum slightly less important in dogs, cats and primates?

Answer 4

This immunoprotection is o also provided by blood exchange through the placenta

Question 5

What does normal milk contain?

Answer 5

¥ contains mostly fat, protein, carbohydrate and water

Question 6

What is the osmolality of milk?

Answer 6

Milk has the same osmolarity as blood: 300 mosmol/l.

Lactose is the principal contributor of osmolarity.

Question 7

What is the pH of milk?

Answer 7

Milk has a pH of 6.6-6.9 .

Question 8

What traces does milk contain?

Answer 8

Milk contains vitamins, trace elements, hormones, ions (Na+, K+, Cl-, HCO3-, Ca2+, Mg2+, HPO42-, SO42-, citrate

Question 9

Epithelial cells in the milk alveoli have high numbers of ………………….. for what?

Answer 9

Mitochondria

The synthesis of fatty acids and non-essential aminoacids.

Question 10

What other organelles are important in the milk alveoli epithelial cells?

Answer 10

RER: synthesis of secretory proteins (Golgi).
SER: synthesis of phospholipids and triglycerides.

Question 11

How Do Compounds Get Into Milk?

Answer 11

Protein (casein) is secreted in the form of granules by exocytosis.
Lactose is secreted with protein.
Lipid (triglyceride) is secreted in the form of membrane-limited lipid droplets by incorporation into the cell membrane. May contain elements from the cytoplasm.
Water follows the lactose by osmotic pressure.

Question 12

How is lipid (triglyceride) synthesised in the mammary gland?

Answer 12

Triglyceride is made from fatty acids in chylomicrons and LDL in the blood.
And from:
glucose (non-ruminants) or acetate and β-hydroxybutyrate (in ruminants).
Pathway of fatty acid synthesis in mammary gland are the same as in other tissues (e.g. adipose tissue).

Question 13

How is lactose synthesised in the golgi body?

Answer 13

Glucose + ATP –> Glucose-6-P + ADP
Glucose-6-P –> glucose-1-P
Glucose-1-P +UDP –> UDP-Glucose –> UDP-Galactose
UDP-Galactose + Glucose –> Lactose + UDP

Question 14

What enzyme is responsible for: UDP-Galactose + Glucose –> Lactose + UDP

Answer 14

Lactose synthase

Question 15

What cells can be found in milk?

Answer 15

Milk contains leukocytes and dislodged mammary epithelial cells.

Question 16

How many cells are in a healthy cows milk? Why is it good to have this many cells in the milk rather than none at all?

Answer 16

In healthy cows: 30,000-300,000 cells/ml.

Too low increases risk of E.coli mastitis.

Question 17

During infection how much does the cell count of the milk increase? why?

Answer 17

During inflammation the number of cells increases 10-100 times
Due to neutrophil invasion

Question 18

What causes involution of the mammary gland?

Answer 18

Involution can be gradual (following peak yield), initiated by loss of young or senile.
Involution involves apoptosis, phagocytes, etc.

Question 19

Where is placental lactogen produced?

Do sows use placental lactogen to stimulate mammary growth?

Answer 19

Produced by binucleate cells of placenta.

Sows have relaxin instead of placental lactogen

Question 20

What hormones stimulate lactogenesis?

Answer 20

Cortisol from a stressed fetus causes a fall in progesterone which releases the prolactin inhibition on the mammary gland.

Question 21

Where is fetal cortisol produced? What is its effect?

Answer 21

Produced by fetal adrenal cortex (specialized cortical cells – not the same regions as in the adult).
Cortisol induces placental enzymes to shift synthesis away from P4 to E2:
Uterus becomes sensitive to oxytocin.

Question 22

Progesterone induces storage of arachidonic acid during pregnancy, why is this significant?

Answer 22

Oestrogen induces phospholipase A, thus arachidonic acid is converted to PGF2α, this leads to luteolysis in species with a CL (bovidae, carnivoridae).

Softens the cervix (aided by PGE).
PGF2α induces myometrial contractions.
Oestrogen exposes myometrial oxytocin receptors.
In primates and equidae, the PGF2α causes myometrial contractions even though P4 still high.

Question 23

Increase in udder volume during pregnancy follows increase in which hormones?

Answer 23

Oestrogen and placental lactogen

Question 24

The density of prolactin receptors is regulated by what hormones?

Answer 24

thyroid, adrenal and ovarian hormones

Question 25

Prolactin regulates the production of …………………..

Answer 25

alpha-lactalbulmin

The enzyme galactosyltransferase binds α-lactalbumin to become lactose synthase.
Progesterone inhibits synthesis of α-lactalbumin therefore inhibits production of lactose.

Prolactin induces synthesis of α-lactalbumin and therefore stimulates production of lactose

Question 26

What hormone is needed for the growth of the golgi apparatus in the milk alveoli?

Answer 26

cortisol

Question 27

Continuous milk secretion is regulated by what?

Answer 27

Hormones in the blood.
Local conditions in the alveoli.
Secretion depends on prolactin.
Release depends on oxytocin.
In ruminants growth hormone can substitute for prolactin.
Insulin and growth hormone regulate metabolism and ensure adequate energy supply to the udder.
Accumulation of milk in alveoli will increase concentrations of Feedback Inhibitor of Lactation.

Question 28

How does the feedback inhibition of lactataion work?

Answer 28

It modulates the synthesis of lactose and milk protein by inhibiting the formation of secretory vesicles in the Golgi apparatus if the milk pressure is too high

Question 29

How does the sucking stimulus cause prolactin release?

Answer 29

Suckling stimulus –>paraventricular nucleus in hypothalamus

This causes an increase in oxytocin and reduction in dopamine which releases inhibition on prolactin release from adenohypophysis.
Increased vasoactive intestinal polypeptide (VIP) stimulates prolactin release.

Question 30

What does the release of oxytocin by suckling cause?

Answer 30

1. Increase pressure in the alveoli.
2. Reduce resistance in the small excretory ducts (myoepithelial cells are oriented along the long axis-ducts become shorter and wider).
3. Reduce resistance in the teat canal.
4. The myoepithelial cells function to squeeze milk out of alveoli into the ducts. They contract in response to oxytocin.
5. Oxytocin improves maternal-neonatal bonding. This is a central effect of oxytocin acting on receptors in the brain.
   Oxytocin also stimulates the cervix to soften and contraction of the myometrium so suckling encourages the rest of the litter to be born

Question 31

What hormone can be used to sustain milk production?

Answer 31

The growth hormone bovine somatotrophin

Question 32

What metabolic changes will the mother make while lactating?

Answer 32

Reduced fat synthesis and increased lipolysis.
Decreased uptake of glucose in muscle and adipose tissue-increased mammary uptake.
Increased uptake of amino acids in the mammary gland (breakdown of muscle protein is not sufficient).
These changes are regulated by prolactin, growth hormone and insulin.

Question 33

How does lactation prevent the oestrus cycle?

Answer 33

Suckling also induces opioid production, which blocks GnRH secretion, preventing ovulation. Weaning removes the suckling stimulus, prolactin is reduced and LH increased.

Question 34

If you fail to milk one quarter, will the whole cow dry up or just that quarter?

Answer 34

Just that quarter

Question 35

What is Galactostasis?

Answer 35

Congestion of the gland combined with oedema and inflammation

Question 36

What is Agalactia?

Answer 36

Lack or reduced milk production

Can be caused by inadequate nutrition or liquid intake, mastitis or other bacterial infections, mineral deficiencies