Reproductive Function in Horses- Lecture 15

Question 1

Characteristics of mares

Answer 1

Puberty 12-24 months.

Seasonally polyestrous.

Question 2

Characteristics of stallion

Answer 2

Puberty 4-5 years.

Functional year round.

Question 3

Long day breeders

Answer 3

Sun –> pineal gland (decreased melatonin) –> hypothalamus (increased GnRH) –> anterior pituitary (increased FSH & LH) –> ovary (increased estrogen & P4).

Question 4

Universal birthday

Answer 4

Jan. 21st.
Physiologic breeding season (April- Sep).
Operational breeding season (Feb-July).

Question 5

Artificial lighting programs

Answer 5

Stimulates daylight.
Accelerates time to first ovulation.
Does not shorten transition: Begins Dec 1st, first ovulation Feb 15th.

Question 6

Estrous cycle of a mare

Answer 6

18-21 days.
Follicular phase: estrus (4-7 days).
Luteal phase: Diestrus (14 days).

Question 7

Follicular phase

Answer 7

Estrus.
Dominant follicle(s) produce estrogen. Ovulates at 40-50 mm at 24-48 hours prior to end of estrus.

Question 8

Luteal phase

Answer 8

Diestrus.
Begins with ovulation.
Corpus hemorrhagicum.
Corpus luteum (progesterone).

Question 9

Autumnal transition

Answer 9

Autumn weather –> pineal gland (increased melatonin) –> hypothalamus (decreased GnRH) –> anterior pituitary (decreased fSH & LH) –> ovary (decreased estrogen & P4).

Question 10

Winter anestrous

Answer 10

Behavior: unpredictable.

Same melatonin chain as autumn.