Lecture 7 -- Reproduction and Lactation in Domestic Animals

These flashcards summarize key concepts regarding reproduction and lactation in domestic animals, based on the lecture notes provided.

How is pregnancy maintained in the bitch (dog)?

Pregnancy relies entirely on progesterone from the corpus luteum (CL) throughout gestation

How is pregnancy maintained in the cow?

• Progesterone from the corpus luteum (CL) is critical in early pregnancy

• By 6–8 months, the placenta takes over progesterone production

• Towards the end of pregnancy, ovarian progesterone resumes an important role

How is pregnancy maintained in the sheep?

• Ovarian progesterone from the CL maintains pregnancy for the first ~50 days

• After which the placenta becomes the primary source

How is pregnancy maintained in the mare?

• Ovarian progesterone from the CL is essential for the first ~70 days

• After which the placenta takes over progesterone production

What are the three stages of parturition?

Stage 1: Initiation of myometrial contractions and cervical dilation

Stage 2: Expulsion of the fetus

Stage 3: Expulsion of the fetal membranes

What initiate parturition?

What happens to progesterone levels before parturition?

Progesterone decreases, removing the 'block' and allowing myometrial contractions.

Explain the Ferguson reflex and its role in parturition

• As the foetus drops lower in the uterus, it causes cervical stretch and activation of sensory receptors in the cervical wall

• This result in a neuroendocrine reflex whereby the signals are relayed via the spinal cord to the hypothalamus

• Stimulate posterior pituitary gland to release of oxytocin

• Oxytocin binds to its receptors in the uterus, and cause release of prostaglandin to uterine wall

• Prostaglandin causes stronger uterine contractions

• There is a positive feedback loop

  • The more the uterus contracts, the more the foetus get pushed into the cervical area -> More sensory input on the it -> More oxytocin -> More prostaglandins -> More contraction

How does the spinal reflex contribute to foetal expulsion?

Local stimulation of the spine triggers abdominal straining, using abdominal pressure to help push the foetus out

Which foetal membrane is usually the first visible structure during birth?

Allantochorion ruptures in the vagina

How does the amnion behave during foetal expulsion?

• The amnion may burst at the vulva

• In some species (mares & bitches) it may cover the foetal head during birth

What is the embryonic origin of the mammary gland?

• The mammary gland is a modified sweat gland

• It is derived from ectoderm

How does mammary gland growth after puberty compare to normal body growth?

Mammary gland growth is disproportionately faster than normal body growth after puberty

What hormone primarily induces mammary gland development after puberty?

1. Oestrogen

   • Promotes duct branching + Increase diameter

2. Progesterone

   • Promotes formation of alveoli at the terminal branch of mammary ducts

3. Prolactin and Growth hormone

   • For more complete and rapid development of ducts

What is the ion composition and major components of milk?

• Protein

• Fat

• Lactose

• Ions: Na+, K+, Cl- and Ca2+

What is lactogenesis?

Lactogenesis is the onset of milk secretion in the mammary gland

Which hormones increase during late pregnancy to prepare for lactogenesis?

In late pregnancy:

• Cortisol

• Prolactin

• Oestrogen

• Placental lactogen

What is the role of progesterone in lactogenesis?

Progesterone decreases at the end of pregnancy

• Low progesterones allows synthesis of prolactin receptor → Prolactin binds to its receptor → Upregulate α-lactalbumin and enzymes needed for lactose synthesis

What is galactopoiesis?

Maintenance of milk secretion after lactation has been initiated

Which hormones are required to maintain milk secretion?

1. Prolactin

   • Maintains alveolar cell metabolism and α-lactalbumin secretion

2. Oxytocin

   • Stimulates myoepithelial cells to remove milk

3. Growth hormone (GH)

   • Supports secretion via IGF-1 in ruminants

4. Indirectly: Insulin, thyroid hormones, and cortisol also contribute

Why is milk removal essential for galactopoiesis?

• Milk must be removed (by suckling or milking) to sustain secretion

• If milk accumulates, secretion stops due to feedback inhibition of lactation

What are the important factor determining milk yield?

• No. of secretory cells in the mammary gland

• Water intake

• Blood supply to the mammary gland

• Milk removal e.g. suckling frequency/ milk frequency

• Blood glucose

  • Decrease blood glucose → Decrease lactose and milk volume

Describe the milk ejection (let-down) reflex.

Step 1: When the lamb is suckling, it stimulates the sensory nerves around the udder

Step 2: The signal travels to the spinal cord through the dorsal root, then to hypothalamus

Step 3: Posterior pituitary gland secretes oxytocin

Step 4: Oxytocin binds to the oxytocin receptors on the myoepithelial cells, surrounding the alveolar cells

Step 5: Myoepithelial cells contract and squeeze the ducts, forcing the milk out