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ASC 410 > Reproductive Biology of Mares > Flashcards

Reproductive Biology of Mares Flashcards

1
Q

Winter anestrus

A

-ovaries are small and hard
-absence of ovulation
-low levels of reproduction hormones (may occasionally show signs of heat though)

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2
Q

Phases of reproductive rhythm of non-pregnant mares:

A

-winter anestrus
-spring transition
-estrous cyclicity
-fall transition

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3
Q

When does winter anestrus begin?

A

late fall (about November)

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4
Q

Spring transition

A

-some ovarian activity
-small follicles (may partially develop, then recede)
-no ovulation
-inconsistent estrus behavior

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5
Q

Estrous cyclicity (the breeding season)

A

-begins with the first ovulation
-regular estrous cycles (estrus and diestrus)
-large ovaries

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6
Q

When does estrous cyclicity end?

A

with pregnancy or with the onset of anestrus

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7
Q

Fall transition

A

-changes in ovarian activity
-hormonal changes (less estrogen from follicles, less progesterone from CL)
-regular cyclicity deminishes
-ovulation ceases, anestrus begins

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8
Q

When does the spring transition begin?

A

early-mid February (about 6-8 weeks after Dec 20th)

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9
Q

When does the spring transition end?

A

late March-early April (lasts about 6-8 weeks)

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10
Q

When does regular cyclicity begin?

A

with the first ovulation after the pring transition

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11
Q

When does regular cyclicity end?

A

mid August to early September

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12
Q

What is the approximate time of the “natural breeding season”

A

regular cycles from late March - early April until mid August - early September

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13
Q

When does the 1st normal ovulation occur?

A

late March - early April
(will then foal in late Feb/early March)

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14
Q

What is the 1st normal ovulation influenced by?

A

natural day length

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15
Q

Natural breeding season is:

A

April into August

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16
Q

Commerical breeding season is:

A

about Feb 15 - mid JuneA

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17
Q

Why start the breeding season sooner?

A

-foals are born earlier (older at yearling age)
-mare has more cycles, more opportunity to breed if cycle is missed
-increases season length/stallions can breed more mares
-spreads out foaling season (reduce crowding?)

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18
Q

Disadvantages to starting the breeding season sooner:

A

-poor weather, mare and foal may not get to go outside enough
-not as high quality pasture
-a spread out foaling season requires longer foal watch (more labor needed for longer)

19
Q

Seasonality is primarily governed by what?

A

day length (and mare body condition)

20
Q

What does day length affect?

A

melatonin production by the pineal gland

21
Q

Melatonin increases during ______

A

the dark

22
Q

Melatonin decreases during ______

A

the light

23
Q

During the winter melatonin concentrations are…

A

elevated for long periods during longer nights

24
Q

What does melatonin do?

A

it suppresses gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus
-low GnRH, cyclicity is inhibited in mares

25
Q

Low melatonin levels allows the hypothalamus to…

A

increase GnRH secretions

26
Q

GnRH stimulates the anterior pituitary to release…

A

follicle stimulating hormone (FSH) and luteinizing hormone (LH) which act on the ovary

27
Q

Advancing the breeding season

A

increase “day-length” (hours of daylight) ahead of natural season

28
Q

What is the goal of advancing the breeding season?

A

to suppress melatonin, allowing GnRH to increase ahead of natural season

29
Q

Increasing day length can be used to:

A

-end winter anestrus sooner
-begin spring transition sooner (may/may not shorten the spring transition period)
-regular cyclicity begins sooner
-total length of breeding season is extended

30
Q

What are the normal hours of daylight in Central KY in late December?

A

about 9 hours

31
Q

What are the normal hours of daylight in Central KY in late March?

A

about 12 hours

32
Q

What is the method to manipulating day length?

A

Impose 16 hours light/8 hours dark
-may increase gradually or just start 16:8
-usually add hours at the end of the day

33
Q

What is the timing to manipulating day length during the year?

A

Initiate 16h light:8h dark in late November-mid December
-allows breeding season to begin mid Feb. (about 120 days)
-instead of early April (natural breeding season) (about 75 days)

34
Q

Mares being kept in a barn for imposed day length:

A

16 hours inside, then outside during the day

35
Q

Advantages of mares being kept in a barn:

A

-highly controlled (cannot access any dark areas in the stall)

36
Q

Disadvantages of mares being kept in a barn:

A

-labor (horse handling and cleaning)
-lots of stalls and lots of bedding
-expense of lights, electric, timer, etc.
-must bring in stall before dark

37
Q

Group lighting for imposed day length:

A

mares are kept in a group outside, in a smaller paddock or dry lot where there are lights surrounding it

38
Q

Advantages of group lighting

A

-less labor; stall cleaning
-less horse handling
-ventilated and social
-don’t need stalls

39
Q

Disadvantages of group lighting:

A

-expensive to build (lights)
-condition of lot (can get muddy)

40
Q

Light mask (Equilume) for imposed day length:

A

mares where a mask that has the left eye open, and the right eye is in a cup with an LED blue light shining

41
Q

Advantages of the light mask:

A

-mares can stay in pastures
-low labor
-cost? (upfront cost could end up equaling cost of bedding/stalls for other methods)

42
Q

Disadvantages of the light masks:

A

-has to stay on the mare
-cost? ($700-1000 each)
-vision? (may not be able to fully see out of the right eye, but no permanent damage that we know of)

43
Q

Imposed lighting, lengthening daylight can also be used for:

A

-stallions (sperm production may be lower in general in the darker months)
-pregnant mares (to try to shorten their gestation length)
-performance horses (some people think it affects their performance and they shed in response to daylight so coat length)

ASC 410 (22 decks)

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