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VM744: THERIOGENOLOGY > Equine Reproduction > Flashcards

Equine Reproduction Flashcards

1
Q

What type of estrus cycles do mares have?

A

Seasonally polyestrus
Multiple estrous cycles during a specific time of the year - April through Oct

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2
Q

How long is a mare’s gestation?

A

340d

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3
Q

What type of placenta do mares have?

A

Diffuse chorionic, epitheliochorial

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4
Q

What are the 4 seasons of mare ovarian function?

A

Winter anestrus (Nov - Mar)
Spring transition
Physiologic breeding (Ap - Oct)
Fall transition period

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5
Q

What occurs during winter anestrus?

A

Inactive of dormant ovaries
Minimal follicular development
Follicles <20mm in diameter
Behavior ranges

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6
Q

How does photoperiod impact seasonal reproduction?

A

Reproductive activity in spring is stimulated by an increasing duration of day length
Mechanism involves an alteration of hormone secretion by the pineal gland and hypothalamus

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7
Q

What occurs during spring transition?

A

Multiple clustered follicles on ultrasound

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8
Q

What occurs during spring transition?

A

Progressive increase in duration of ambient photoperiod
2-3m duration
Occurs when first developing follicle reaches 20-25mm
FSH results in 1-3 waves of follicular development and regression
Late transition in reference when one or more follicles are >30mm

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9
Q

Behavior during spring transition

A

Prolonged or irregular periods of estrus in response to estrogens produced by developing follicles
Eventually one dominant follicle of a late-transitional phase ovulates

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10
Q

What is the average date of the first ovulation of the year in CO?

A

May 1st

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11
Q

When is the physiologic breeding season?

A

April - October

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12
Q

How long is a mare interovulatory period?

A

21d

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13
Q

How long does estrus last in mares?

A

5-7d

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14
Q

How long does diestrus last in mares?

A

14-16d

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15
Q

What occurs physiologically during estrus?

A

Follicular growth resulting in ovulation (growth = FSH, ovulation = LH)
Rising levels of estrogen
Low levels of progesterone
Mare is receptive to stallion

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16
Q

How much does a dominant follicle grow per day?

A

3-5mm/day

17
Q

What hormone causes the mare to come into heat?

A

Estradiol (in the absence of progesterone)

18
Q

What occurs physiologically during ovulation?

A

Secretion of LH causes maturation of follicle and ovulation
Ovulation occurs as follicular wall ruptures
Blood clots to form corpus hemorrhagicum

19
Q

What occurs physiologically during diestrus?

A

Minimal estrogen and high progesterone blocks behavioral estrus
Mares are unreceptive to stallion
Secretion/development of endometrial glands altered and cervix closes
CL is maintained (if pregnant) or lysed to allow the mare to come back into estrus

20
Q

How long is the duration of luteal function in mares?

A

14-16d

21
Q

What hormone causes destruction of the CL?

A

Prostaglandins
Can give prostaglandins early in order to short-cycle

22
Q

When does postpartum estrus occur?

A

First ovulation occurs 9 to 10d after foaling

23
Q

What occurs during fall transition?

A

Irregular waves of follicle development
Regression without ovulation

24
Q

Behaviors: Estrus

A

Raising tail
Passive urination
Winking
Mating posture

25
Q

Behaviors: Diestrus

A

Pin ears
Kick
Switch tail
Vocalize
Move away from stallion

26
Q

Estrus Detection Problems

A

Traditional mares: may be in estrus but not cycling
Silent heat mares: maiden mares
Foaling (‘wet’) mares

27
Q

How do we monitor the estrus cycle?

A

Diameter/growth patterns of largest ovarian follicle through palpation and u/s
Presence/absence of CL
Uterine edema pattern
Uterine/cervical tone
Cervical characteristics

28
Q

How can we manipulate the mare repro cycle with hormone therapy?

A
29
Q

When does an imposed breeding season begin?

A

Early feb

30
Q

How can we stimulate follicular growth?

A

Light therapy late nov/early dec for ovulation in early feb
60-70d required
16h light, 8h dark

31
Q

Advantages: Pasture Breeding

A

Decreased horse handling
Decreased expenses for personnel
Decreased breeding expenses

32
Q

Disadvantages: Pasture Breeding

A

Potential injury to mares and stallions
Inability to detect repro problems
Spread of disease
Lack of accurate conception dates and foaling calendar

33
Q

Advantages: Hand Mating

A

Breeding scheduled
Mare examined to confirm ovulation
Less risky to stallion
Dismount sample collected

34
Q

Disadvantages: Hand Mating

A

Time required for examination/teasing mares
Number of personnel
Risk for injury to personnel

VM744: THERIOGENOLOGY (31 decks)

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