Estrogens (high during estrus, baseline during diestrus) do enhance estrous behavior, but are often not necessary for the mare to show signs of estrus. Progesterone is produced by the corpus luteum and exerts a strong inhibitory effect on estrous behavior, making diestrous mares strongly averse to the advances of the stallion. The most important hormone regulating estrous behavior in the mare is progesterone. The mare will be reluctant to approach the stallion. A mare in diestrus will generally clamp her tail down tight over her vulva, keep her ears pinned back, squeal, and kick out to strike. The mare may squeal, playfully kick out (not to strike), or turn to push her hind end towards the stallion. The ears are alert and generally forward. Whether she is showing behavioral signs of estrus ("teasing in") or not ("teasing out") can be the deciding factor as to how you should proceed with her protocol.īehavioral signs of estrus in the mare classically include raising the tail, squatting, everting the clitoris ("winking"), and urinating. With all of these variables, it is often useful to be able to take a mare sending mixed signals through our routine reproductive examination and expose her to a stallion. The cervix generally softens during estrus, but maiden mares will often have a tight cervix throughout their cycle. Follicles generally reach a certain size before they ovulate, but diestral follicles can reach those large sizes and then regress instead of ovulating. Ultrasound allows us to monitor uterine edema, a very useful tool in monitoring the mare cycle, but inflammation can also cause edema. Even with the technical advances of our day, including ultrasound and hormonal manipulation, the mare's natural reproductive behaviors still play an important role in determining if and when to breed her. The earliest form of breeding management in horses was simply to tease the mare to the stallion and allow them to breed periodically while the mare showed signs of being in heat. No matter what protocols you develop, the end goal is the same: foals on the ground the following year. It is up to you to figure out how to effectively use those tools to manipulate the cycle around whatever unique parameters surround your particular farms. This lecture will focus mostly on the normal physiological changes in the mare reproductive cycle and how we can manipulate the cycle. All of these variables will influence your decisions about when to schedule follow-up examinations, when to give certain drugs, when to inseminate, etc. These should include the type of semen or breeding used (live cover, fresh AI, chilled/shipped AI, or frozen), when the stallion (or semen) is available, if the mare is to hold the pregnancy or be an embryo donor, if the mare is to be bred on foal heat, your availability to that farm (Do you visit every day? Do you work weekends?), and perhaps other factors unique to that particular farm. When designing breeding management protocols for a particular mare or stud farm, you must take into account many external factors. With some minor breed differences, most mares have similar reproductive physiology and, from that respect, may be expected to respond similarly to a canned breeding management protocol.
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