We short cycled my mare last week and the follicle was HUGE when the vet checked after the initial short cycle shot (estro…something). Vet said it was much bigger than it ‘should’ have been. How big are they supposed to grow each day?
Sometimes it depends on where in the cycle of diestrus they are when you short cycle them. If you short cycle them very closely to the 5 days after ovulation, then they usually have an ovulatory follicle within 5-7 days (ie, ovulate). But if you short cycle them towards the end of diestrus (when they might have some 20 mm follicles), they can go much faster (say ovulatory follicle in 4-6 days).
I usually give prostaglandin F-2-alpha (or Estrumate) late on a Friday night (say 10pm) or early Sat morning for most mares and check on Monday late morning/early afternoon (depending on the collection schedule of the stallion and my vet’s schedule).
But one mare I gave it on a Sunday AM and checked Tues AM because she goes faster than my other mares and can have huge breedable follicles in a short period of time (learned that last year). By Tuesday she had a 32 and we bred on Thursday and she ov’d that night with hCG.
As far as growth per day, depends on the size of the mare/breed, possibly, but we estimate 3-5 mm/day.
Ditto what Kris said - we normally give lutalyse on Thursday PM and check Sunday PM or early Monday AM, early in the year. This puts us usually ordering on Tuesday or Wednesday and they ovulated Wednesday or Thursday, ocassionally Friday. Later in the year, it definitely goes quicker; we gave it Thurs and then checked the mare Sunday PM and she had a soft 55mm follicle and little edema left, almost ready to ovulate… holy cow! So we had to short cycle again 
And yes, usually ours seem to do as much as 6-8mm a day growth as the summer goes on, but normally closer to 4-5 during the earlier spring.
Depends on the season. I just missed a mare who was about to ovulate 3 1/2 days after estrumate. Next time round we gave it on Saturday and yesterday she had a 31 x 33. We u/s again today and are expecting to call for semen today.
[QUOTE=back in the saddle;5714814]
We short cycled my mare last week and the follicle was HUGE when the vet checked after the initial short cycle shot (estro…something). Vet said it was much bigger than it ‘should’ have been. How big are they supposed to grow each day?[/QUOTE]
If the mare is given prostaglandin when she has a mid-cycle follicle, she may come into estrus and ovulate very quickly. On average, when prostaglandin is given, the mare returns to estrus 3 to 5 days after receiving the shot and usually ovulates 7 to 9 days after receiving the hormone. Mares grow a follicle, on average, 3 to 5 mm a day.
Edited to add article link: http://www.equine-reproduction.com/articles/Prostaglandin.shtml called “I gave my mare prostaglandin, but it didn’t work! (aka why prostaglandin use may not result in estrus in mares)”
Hope that helps!
Kathy St.Marrtin
Equine-Reproduction.com, LLC
http://www.equine-reproduction.com
