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Equine Repro Man

There are other ways to tell if you mare is in heat besides noticing that special gleam in her eye. Pay attention to that dark brown mass hanging from the brown iris. That's the corpora nigra. It'll be talking about that in another blog.

Tina was the repro tech for Creston Oaks Arabians. Each mare needed to pass a pre-breeding exam before going into the artificial insemination lineup. Mares are seasonal reproducers, February was the time of year they begin to cycle, especially if they have been subjected to an increasing light regimen starting around Christmas.

A mare's cycle is shorter than a woman's, lasting three weeks, but she only shows real evidence of heat for about five of those days. Think about it this way: the mare is in season for the better part of a week, followed by sixteen days out, then the cycle repeats.

Mares ovulate about the fifth day of the cycle, but how do you know the cycle has started? From the change in behavior she's showing; her hormones are pushing her to start a quest for a baby. She's totally focused on getting bred, and that means you are now second fiddle in regards to things like dressage training. Even trail riding with the cowboys is irritating if someone's mare can't settle down at least one minute during the entire trip.

Just before coming into season and often for the first few days they are showing signs, some mares are irritable and sensitive to touch. They may threaten to kick or even bite. Part of this is because the hormonal changes are making her focus elsewhere so that she is more easily startled. Pressure pain from the enlarging follicle and pulsations in the ducts that will carry the egg to the uterus are also likely involved, but this is a second-hand guess, I don't get periods.

Typical signs a mare is in season include holding the tail elevated; we call this flagging. And we look for winking; the mare stands in a peculiar stance, her hind feet farther apart than normal, assuming a position ready to urinate, but only a small amount of urine comes forth. Visible cues come out instead of urine; she's winking; opening and closing the lips of her vulva.

This girl is flagging and winking.

Her tail goes straight up, and her vulva plays peek-a-boo.

She is ready to be bred

All these signs are due to the new hormone estrogen, flooding the mare from her growing follicle pushing her into heat. This estrogen-induced flamboyancy intensifies over a few days then stops abruptly after she ovulates. These are the signs of being in full-blown heat.

Normally mares come into season between April and September, shutting down repro activities in the winter cold. For a few months on either side of that the ovaries are transitional, they are in the process of either gearing up for spring or slowing down for winter and may produce one or multiple non-performing follicles at random times. During these spring and fall transition periods the mare may or may not show signs of being in season.

Horse breeders a focused on having a baby born as close to January or February as possible. Why? Because it makes a difference in competition among the youngsters.

Say two horses are racing in a claiming race for two year olds. That means that this category will contain horses as young as twelve months plus a few days to as old as twenty-four minus a few days, which is quite a difference when running races for prize money. That’s why high stakes breeding programs try to get mares pregnant in February or March instead of September, and this can be done artificially by manipulating the lighting periods the mares are exposed to. In esssence we are tricking the mare’s brain to make it think the season is later than it is by leaving the light on in her stall longer.

Once Tina identified a horse as coming into estrus she called me in for a pre-breeding exam. The breeding shed is a two-room affair: the lab, and the horse room. Obviously, the horse space is the largest; there is a metal pipe cage with swinging doors where the mare stands comfortable and accessible for procedures. And in the other corner is a dummy mare set in a permanent receptive pose, basically a barrel attached to a pole, with gimmicks and pretties attached. And to enhance the ambiance, the entire shed is paneled in knotty pine wood.

Anyway, Tina would find a mare in heat and call me to perform a uterine culture, cytology, and biopsy. If all those tests came back normal, we'd short-cycle her the middle of her next cycle, setting her in line for AI, artificial insemination.


The dummy mare is in the foreground. The real mare is in the distance. This place is definitely low-rent; there is no paneling on the walls, and the dummy mare isn't even decorated. In some places a makeshift head is attached up front, along with a petty smile and big eyes with long eyelashes painted on.






Audiobook coming soon



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