Explaination Pleas

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Well-Known Member
Dec 21, 2005
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North Texas
Has anyone had this before?

Can someone tell me how this happens in lay terms?

I had a mare that had a prolonged heat cycle. I took her to the vet and this is what she was diagnosed with. But of course the questions didn't enter into my mind of "how does this happen and why" till I left. She did receive a shot to help her cycle. But the vet advised that he didn't think the follicle would be viable. Why would this be? He suggested that I wait till her next heat cycle.

I appreciate any help. I am sure everything will be fine I just would like to have a better understanding and all the websites I visit are so technical.

First off, I am not a vet, but this is what I know from my equine repro class and what I just researched online:

A follicular cyst is a fluid-filled 'structure' that develops in the ovary. It results in prolonged excretion of estrogen (which is what caused your gal to have a prolonged heat cycle)

I tried to look up some information but wasn't able to find a definite cause as to WHY, but from what I have read, it may be due to ovulation failure (so the follicle continues to enlarge) or failure GnRH (gonadotropin-releasing hormone) release or possibly to deficiency of LH and/or follicle stimulating hormones in the developing follicles.. (confused yet!?

Did your vet recommend giving her any hormones to cause the follicle/cyst to regress?
Persistant Anovulatory Follicles (PAFs) are follicles which just won't ovulate. They cause significant output of either estrogen or progesterone (depending on where they "hung" in the process of ovulation). Those hormones can cause them to be persistantly in heat or persistantly out of heat, respectively. Several treatments can be effective with theses.

1) TIME. Eventually they will resolve them on their own.

2) An ovulation-inducing drug, such as hCG or Deslorelin, if the follicle can respond to the "ovulate" command.

3) A CL killing drug such as Estramate or Lutalyse, if the follicle has partially ovulated or has CL-type cells.

Easily confused with PAFs, but completely different, are follicular cysts (which are completely different from human follicular cysts or equine uterine cysts). They look very similar, are solid tissue (PAFs can be fluid filled), and produce testosterone. These do not resolve on their own, and do not respond to drugs. The only treatment for true cysts is surgical removal of the effected ovary. This will not effect their fertility since the other ovary will still produce fertile oocytes. They are very rare, and are constantly confused and misdiagnosed.
I do appreciate the information. I think I am a little clearer on the issue.

The vet did give her the hCG. However I did breed this mare yesterday (late) and if we go on the assumption that the sperm will live 2-3 days, could she still catch? And what would the implications be if the vet feels that the egg isn't viable. Will she just not take?
I would be very surprised if she takes on this follicle -- hopefully the HCG will cause the follicle to regress or "ovulate" and then in around 16 days she should be back in & hopefully will have a "normal" cycle.

Keep us posted, this type of information is always very helpful.

I certainly will keep you all posted on the progress.

Interestingly enough I actually took two mares in because they had the same pattern. Both have been showing heat for 55 days.

Of course the one had the cyst but the other was 20 days bred and has been accepting the stallion and showing full blown heat for all those 20 days.

And also another interesting fact that kind of goes with another thread is that this mare that is bred has shown the stallion like behavior since she came into heat.

The other mare with the cyst just started doing the same thing last week. I thought it was a learned behavior from watching her best friend in the pasture. But now by reading through some other threads maybe it was the cyst that caused the hormonal changes that caused the behavior.

And certainly don't let me forget to thank all for the detailed explainations.
There is a chance that she may get in foal, especially if the hCG works as "designed". Sperm can live for some time in the mare's body, so 2-4 days isn't unreasonable to hope for. But if she's been holding this PAF for some time now chances are the oocyte inside the follicle is dead. Once the PAF clears up things should be back to normal. Some horses will do this many times though, sometimes every cycle. I knew one mare who ended up having her ovary removed because the same one PAF'ed every cycle all year long. She now is a successful broodmare with one ovary.
Well a quick update on my mare that had a cyst.

She hasn't come back into heat. So my thought is that she slipped through with a pregnancy as I bred her the night before she got the shot to remedy the cyst.

Well took her for an ultrasound to see what was going on. She has a small amount of fluid in her uterus but not enough to confirm a pregnancy.

Vet wants to wait a couple weeks to see if it will develop into a pregnancy or if it is a slight infection. So everyone keep your fingers crossed.

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