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Breeding Shed

“Reproduction is the most basic, strongest drive your horse has - even to the point of taking precedence over eating. Small wonder then that your mare’s reproductive cycles may produce pretty obvious signs, and her attention when in season (“heat”) is not primarily focused on you. Understanding what’s going on, and the timing, can help you deal with it more effectively.”


Mares typically cycle regularly between April and early September. For a few months on either side of that, the ovaries are in the process of either gearing up for spring or slowing down for winter and may produce one or multiple follicles at irregular times. During these spring and fall transition periods, the mare may or may not show signs of being in season. Reproductive behavior is most likely to be noticed during the fertile period between April and September.

A mare's cycle is shorter than a woman's. The average length is three weeks, with most falling within the range of 18- to 23-day cycles. The mare will be in season ("show heat") for an average of five days during each cycle, with a range of three to seven or eight days. Many people complain that their mare is in season every two weeks and think that's abnormal, but it's not. The normal cycle is for the mare to be in season for the better part of a week, followed by two weeks out, then another week or so in.

I unsheathed a vaginal speculum, a twelve-inch long reflective cardboard tube. That and a flashlight allowed me to be into the vagina, the first abyss behind the vulvar lips. Pointing the flashlight beam along the long silver tube, I pushed the speculum straight forward and a little down looking for the cervix, it was the primary structure in the vagina, looking like a round mound of tissue with a hollow center, the os, or opening into the uterus. (Fear of Failure Ch.33) This mare's cervix was floppy and flaccid, leaning downward as if it were tired, or hiding the os from the penis maybe, in a kind of hormonal pretease? (Picture)

Typical signs that the mare is in season include holding the tail elevated, "winking" (opening and closing) the lips of the vulva and variable amounts of squatting and squirting of urine and mucus. A mare's level of activity usually slows down a bit, and she often seems preoccupied. It's more difficult to get and hold her attention, because frankly you're not the most important thing on her mind at the time. These are the signs of being in full-blown "heat," which will intensify gradually over a few days, then stop abruptly after she ovulates.

Just before coming into season, and often for the first few days they are showing signs, some mares are very 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-like pain from the enlarging follicle and/or pulsations in the ducts that will carry the egg to the uterus are also likely involved.


Last: Palpating Ovaries

Next: Fall Concert


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