Transition heat cycle

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Well-Known Member
Sep 19, 2007
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Please tell me about transition heat cycles-- is there actually an egg released or is this just a 'practice run'. One mare wasn't around a stallion until three weeks ago and she went into a major heat type behaviour at that time. The stallion bred her during that week. Then, in only two weeks time, she was back in heat. So, I am quite curious.

Also, from other threads I have learned that a fertilized egg can float around for up to 40 days before being planted in the uterus. If this happened, by chance, could the mare go back into heat like this one did?

Once the egg implants they are "settled" so she shouldnt come back in her cycle. But that doesnt always mean anything LOL

we have a mare here now who bred every cycle all summer. I finally gave up and stopped breeding her in Aug. I really thought she didnt settle. Did a urine test and was shocked to see she was in foal. Well looking at her huge belly she obviously was settled and kept breeding. I hate it as now I really dont know when shes due but looks to be around the end of May.

Some mares just drive you crazy
My mare hadn't seen a stallion for a few years. I had her bred for this year and we were afraid she was having a transitional heat as she wasn't settleing. She lasted for 13 days, and was bred about every other day, before finally coming out of it. I really believe that from being away from one for so long and then coming into a farm with other mares she just stayed into heat for a long period of time.
Transitional heat cycles happen in the spring and fall when the sun causes a hormonal change in the mare's brain. This hormone starts a cascade of other hormones which tell the mare to start building a follicle. However, the first few times she doesn't produce enough of the hormones to cause the follicle to ovulate. As the hormones wain, the follicles die and go away. Since the follicle never actually ovulates, no CL is formed and therefore there is no progesterone to tell the mare to go out of heat. Since follicles produce estrogen, which tells a mare she's in season, as the mare comes and goes out of heat she will cycle between actively seeking a stallion and being indifferent (but usually still allowing him to breed if he wants).

The long, long heats typical of spring transition are caused by the small amounts of estrogen and no progesterone. Once she ovulates for the first time of the year, she will generally start cycling normally. Until she ovulates, no pregnancy is possible.

As far as the "floating" idea, yes, that is true. For about 20 days, the embryo will migrate around the uterous. This is MANDATORY for pregnancy. If the embryo doesn't move around the mare will not recignize herself as pregant. Once the embryo is large enough to get "stuck" in the folds of the uterous, it will remain independant for an additional 20ish days. Around 35-40 days it will formally attach. However, it is the period around 20 is when the mare officially recignizes herself as pregnant, and keeps her CL intact. This CL produces progesterone, which keeps her out of heat and acting like she's pregnant. It starts producing its hormone a few days after ovulating the egg. If that embryo can not move around enough, she will kill her CL and start building a new follicle with a new oocyte (egg).
Good thread.

It seems that all my mares are in heat this week. I don't like to breed until the end of May so that my foals are born in the nicer weather.

Do you consider end of April a transitional hit? It seems that some of them have been in a long heat now.


Mid May through mid July is the mare's natural physiological breeding season in the northern hemisphere. So to have a transitional mare in April, while not common, is completely normal. Many mares will start cycling in March and April but there will definately be some mares running behind. The peak is in May-June-July.

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