Abstract
With an understanding of basic reproductive science, veterinarians and breeders can be better positioned to achieve their goals. It is important to understand the heat or estrus cycle in order to maximize the chances of success when breeding the mare. Reproductive activity in horses is seasonally dependent, as it is primarily affected by the length of daylight. Therefore the mare has a seasonally polyestrous type of estrous cycle. This means they have breeding season in which they have multiple heat cycles, is receptive to the stallion and ovulates; and a period where they will not go into heat or anestrus. During the anestrus period, most mares show no behavioral signs of sexual receptivity and fail to develop follicles that ovulate. There are exceptions in that a small percentage of mares that do not express a seasonal pattern in that they stay both behaviorally and physiologically receptive to stallions throughout the year. During the ovulatory season, the mare is cycling, thereby exhibiting sexual receptivity to the stallion on a regular basis and is producing follicles that ovulate. The equine estrous cycle is commonly described as a combination of a follicular phase, or estrus, and a luteal phase, or diestrus. The endocrinology of the estrous cycle involves a balance between hormones produced by the pineal gland, hypothalamus, pituitary gland, ovaries, and endometrium. Growth of antral follicles in the ovary occurs in wave-like patterns, and is influenced by several factors such as stage of the estrous cycle, season, pregnancy, age, breed and the individual. In this article will describe the neuroendocrine mechanisms related to breeding seasonality, the hormonal changes that occur during the estrus cycle as well as the variations among mares in regards to the understanding the physiological mechanisms related with the estrous cycle in the mare
Highlights
The mare is a “seasonally polyestrus” female, meaning that she undergoes regular estrus cycles during a portion of the year and none at others
Diestrus or the luteal phase is dominated by progesterone produced by the corpus luteum has a duration of day or day
It is important to understand that there is a closely linked feedback system between many of the reproductive hormones present in the mare which will alter the level or presence of some hormones as levels of other different hormones increase or decrease. This means that many hormonal changes do occur naturally, but when something becomes unbalanced either naturally or artificially, we can see estrous cycle problems develop in the mare
Summary
The mare is a “seasonally polyestrus” female, meaning that she undergoes regular estrus cycles during a portion of the year and none at others This is nature’s way of preventing the arrival of a foal during bad weather. It is important to understand that there is a closely linked feedback system between many of the reproductive hormones present in the mare which will alter the level or presence of some hormones as levels of other different hormones increase or decrease. This means that many hormonal changes do occur naturally, but when something becomes unbalanced either naturally or artificially, we can see estrous cycle problems develop in the mare. To be successful in the breeding of horses is essential that owners of mares and technicians understand the reproductive cycle of the mare
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