Lactation

Question 1

When does mammary gland development begin?

Answer 1

Whilst the foetus is in utero - teats can be seen on an ultrasound

Question 2

What is the predominant dairy breed?

Answer 2

Holstein

Question 3

How how the dairy herd yield been increased progressively despite the number of farms decreasing?

Answer 3

• Improved genetics (AI)
• Improved nutrition
• Improved technology

Question 4

Why had yield advanced the most amongst dairy breeds?

Answer 4

It has the highest heritability

Question 5

What are some of the main problems associated with lactation?

Answer 5

• Decreased fertility
• Compromised immune function
• Increased lameness
• Mastitis
• Metabolic stress

Question 6

What are the 3 major components of all milks?

Answer 6

Protein
Fat
Lactose

Question 7

What are the major proteins of milk and where are they found?

Answer 7

Caseins - found in the curd

Question 8

For how many days is milk withheld for human consumption following parturition?

Answer 8

4

Question 9

Colostrum provides what type of immunity?

Answer 9

Passive

Question 10

What are the components of colostrum?

Answer 10

• high in fats, protein, and vitamin A

- low in lactose

Question 11

Describe the embryology of mammary glands

Answer 11

• Two parallel lines of ventro-lateral ectoderm in the embryo
• Develop into thickenings known as mammary band
• Mammary buds grow into underlying mesenchyme
• Mammary glands = epithelial

Question 12

What occurs following the removal of a wrong supernumerary teat?

Answer 12

1/4 of the udder won’t be able to release milk

Question 13

What anatomy makes up the mammary gland?

Answer 13

• Teat/nipple and associated ducts

- Alveoli, secretory cells and supporting tissues

Question 14

Which structure separates the gland cistern from the teat cistern?

Answer 14

Annular fold

Question 15

Which ligaments form the suspensory system attaching the udder to the body?

Answer 15

• Median suspensory ligament

- Pre-pubic and sub-pubic ligaments

Question 16

Describe the structure of the gland

Answer 16

• secretory tissue (parenchyma)
• ducts
• storage sinus (cistern) lying in a fat pad
• terminating externally in a teat or nipple

Question 17

What is the function of the cistern between the teat and udder?

Answer 17

Large cavity where milk can collect between milking

Question 18

Despite the presence of large cisterns, where is most of the milk actually stored?

Answer 18

Alveoli

Question 19

The alveolus is a basket like arrangement of what type of cells?

Answer 19

Polarized epithelial secretory cells

Question 20

What surrounds the polarized epithelial secretory cells in the alveolus?

Answer 20

Myoepithelial (smooth muscle) cells and blood vessels

Question 21

The number of secretory cells is a prime determinant of what?

Answer 21

Milk yield

Question 22

Until puberty mammary tissue grows at what rate?

Answer 22

Same as the rest of the body - isometric growth

Question 23

Following puberty/oestrus cycle, at what rate does mammary tissue grow at?

Answer 23

Faster than the rest of the body - Allometric

Question 24

How do mammary cells change from gestation to the end of lactation?

Answer 24

• Secretory cells proliferate during gestation
• Some proliferation in early lactation, but mainly differentiation
• Gradual involution (apoptosis) during declining lactation
• Rapid involution after drying off or weaning

Question 25

Which hormones cause growth of ducts?

Answer 25

Oestrogen + growth hormone + adrenal steroid

Question 26

Which hormones cause milk secretion?

Answer 26

Prolactin + adrenal steroids

Question 27

Describe stage 1 and 2 of lactogenesis

Answer 27

1. Acquisition of secretory capability pre-partum | 2. Onset of copious secretion at around parturition

Question 28

What is the main hormonal requirement for the onset of lactogenesis?

Answer 28

Progesterone withdrawal

Question 29

How does the foetus syncronise stage 2 of lactogenesis with parturition/milk production?

Answer 29

- The foetus signals from its own hypothalamus and pituitary to secrete cortisol from the adrenal gland - This passes across the placenta and increases oestrogen levels - This stimulates PGF2a release from the uterus - This goes to the ovaries causing luteolysis of the CL, and a decline of progesterone - This stimulates labour and production of milk

Question 30

Teat stimulation evokes which reflex?

Answer 30

Neuroendocrine reflex - develops positive pressure in the udder

Question 31

Describe the milk-ejection reflex

Answer 31

- Teat stimulation causes afferent inputs to go to the hypothalamus - Causes oxytocin to be released from the posterior pituitary - Leading to contraction of myoepithelial cells in the mammary gland

Question 32

Describe a milking routine

Answer 32

- Clean teat (pre-dip or wipe) - Inspect for clots - foremilk - Leave for 30 seconds to allow for oxytocin action - Cluster on - Milk flow reduced - Cluster off - Post milking teat dip applied

Question 33

What is galactopoiesis?

Answer 33

Maintenance of established lactation

Question 34

Continued milking does 2 things, what are they?

Answer 34

- Stimulates the release of galactopoietic hormones | - Prevents milk stasis

Question 35

How is the drive for lactation different in cows to most species?

Answer 35

- In cows it is GnRH driven | - In most other species it is prolactin driven

Question 36

What is BTS and why is it now banned in the EU?

Answer 36

- Method that significantly increased milk yield of dairy cows - But had serious consequence on health and welfare

Question 37

What 3 things inhibit apoptosis?

Answer 37

- Prolactin - GH - IGF1

Question 38

What 2 things stimulate apoptosis?

Answer 38

- Weaning | - Milk stasis

Question 39

How long is the optimal dry period?

Answer 39

60 days