Equine 1 Flashcards by Marin Low

when do horses cycle?

from spring to fall so they don’t give birth in the winter (long day breeders)

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how long is the estrus cycle in the mare?

21 days

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how long is diestrus in the mare?

14 days (fixed duration)

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in the mare, does ovulation occur before or after estrus behavior?

1-2 days BEFORE estrus behavior

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when are most horses bred?

April or May

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what is “transition”? why should I care?

period of time when ovaries transition between estrus and anestrus. During transition periods you can’t breed the horse so this can delay breeding, and the behavior of mares during this time can be problmeatic for owners

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what does it mean if the uterus shows edema and looks like a star on ultrasound?

it means it is under the influence of estrogen–>estrus? i need to fact check this

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how many follicular waves do mares have?

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the corpus hemmhoragicum turns into

the corpus luteum

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what does a CL look like on ultrasound of the ovary? If you see one, what does this mean?

look more hyperechoic than ovarian parenchyma. if you see one, it means the horse has already ovulated and they’re in diestrus

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how big does a follicle have to be before the mare ovulates it? when do they ovulate?

40-50mm
24-48 hours before end of estrus

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what are examples of estrus behaviors?

squealing, excessive urinating, clitoral winking, tail raising, posturing with wide hind legs, back pain, grumpy or cuddly, etc

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role of melatonin in the horse estrus cycle?

melatonin decreases with increasing daylight, #1 most important controller of seasonal polyestrus breeders! with low melatonin, GnRH increases. You can create artificial light for horses to help them transition!

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role of GnRH in horse estrus cycle?

released from hypothalamus, stimulates pituitary to release FSH & LH

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role of FSH in horse estrus cycle?

made by anterior pituitary, pushes mare out of transition in spring, stimulates follicular growth. peaks in diestrus, can have 2 follicular waves!

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why do diestrus follicles usually regress in the mare?

to help select one follicle–>we don’t want twins!!! (placental insufficiency)

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what role does inhibin play in horse estrus cycle?

inhibin is produced by granulosa cells of the dominant follicle and acts as neg feedback for pituitary, aka, inhibits FSH, making sure only one follicle develops

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role of estrogen in horse estrus cycle?

made by mature follicles nearing estrus and stimulates behavioral response, also relaxes the cervix, increases edema of the uterus, vag, and vulvar lips, increases smooth muscle activity in uterus to help transport sperm. tells pititary to stop FSH and send LH

the role of LH in horse estrus cycle? When does LH peak?

released from pituitary gland, helps to mature the dominant follicle and prepares to ovulate. LH peaks 2 days post ovulation

the LH surge in a horse can be influenced by

teasing /stallion contact

the LH surge only works on follicles that are what size?

greater than 35mm

role of progesterone in horse estrus cycle

produced by the CL, increases after ovulation, inhibits further estrus, prepares uterus for pregnancy, makes cervix tight

what are some ways you can use progesterone (think of what it does)

can give progesterone to maintain pregnancy, or to stop their cycle like in sport horses that need to focus

role of prostaglandin in horse estrus cycle? clinical relevance?

produced by endometrium, destroys the CL/reduces progesterone, allows for another FSH cycle to begin

can give to horses to kickstart ovulation again, or give to them when CL is present/theyre in diestrus and you want them to cycle

what are some parameters we can use to predict ovulation in the mare?

follicular diameter: 35-60mm uterine edema: max 24 hours prior to ovulation follicle shape: will be pointy/angulated thickening follicular wall softening of the follicle by involution

what parts of the mare estrus cycle can be manipulated?

- can short cycle w/ prostaglandins in diestrus (kill the CL) - ovulation - can prolong diestrus w/ progesterone - transition into spring with artificial light

how do you induce ovulation in the mare with HCG? what things do you need to remember?

human chorionic gonadotropin (HCG) can induce ovulation--> it has LH action and can mimic LH surge the follicle has to be greater than 35mm in diameter or it wont work, and the mare will on average ovulate 36 hours after administration also is a bit controversial, horses can develop antibodies to this and can cause anaphylaxsis-->do not use more than twice per breeding season

what other drug can you use to induce ovulation in the mare? How does it work and what are things to remember?

GnRH analogues like Deslorelin. It causes endogenous LH to be released. Can be given on 30-40mm follcile. Ovulation happens 40 hours later. This is a single injection

What can you use to interrupt diestrus/short cycle a mare? When is this contraindicated?

PGF2 alpha such as Dinoprost "lutalyse"-->causes luteolysis. The CL responds 5 days after ovulation do NOT give to pregnant horse! always check before giving!

what are the cons of using Dinoprost to short cycle a mare?

it makes the horse sweaty and causes uterine contractions, can appear like colic

what drug can you use to prolong diestrus? what is one important thing you need to remember about this drug?

Using exogenous progesterone analogues, such as Regumate/Altrenogest. Can manage the transition period, predict estrus during show season, and to suppress all estrus activity remember: you can absorb this thru your hands! wear gloves!

true or false: horses dont get cystic follicles

true

which transition period can you manipulate?

the spring transition: can provide artificial light +/- regumate CANNOT manipulate the fall transition

what are some "issues" with the spring transition?

irregular estrous periods, prolonged heat periods, heats without ovulation (anovulatory dominant follicles)

what is an "autumn follicle"?

a follicle with large diameter that persists during fall transition with no concurrent uterine edema or signs of estrus

how do you provide artificial light to help with spring transition? be specific

the horse needs 16 hours of light and 8 of dark, and the light needs to be added on to the end of the day not the beginning. Takes 6-8 weeks to show effect and then transition starts. Traditionally you can start this December 1st

which horse species develop larger follicles?

warmbloods, up to 60mm

fresh cooled semen is viable for

48 hours-->remember to check viability before inseminating! could be dead!

how long are oocytes viable for?

12 hours after ovulation-->ideally you breed 12 hours BEFORE ovulation

sperm need how long to travel to the oviduct?

6 hours

how should you decide when to inseminate?

fresh cooled semen good for 48 hours, takes 24 hours to ship, and you want to inseminate 12 hours before ovulation. If you see your mare has a large enough follicle, you could give HCG or Deslorelin, then inseminate 24 hours later! If all goes to plan the horse should ovulate 12 hours after inseminating.

why should you always do a post breeding ultrasound 24 hours after insemination?

to make sure the horse has ovulated or to check for fluid/post breeding endometritis

when can you detect pregnancy?

12-14 days is the earliest you can see an embyro on ultrasound but ideally check at 16 days-->to make sure there's not twins and if there is, you need to pinch one

what is the danger of pinching a twin?

can cause enough inflammation to kill the other embryo. can prevent this by giving progesterone to maintain the CL/pregnancy