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The cow estrous cycle typically lasts 21 days. [5] Standing estrus is a visual cue which signifies sexual receptivity for mounting by male cattle. This behavior lasts anywhere between 8 and 30 hours at a time. [26]
This cycle contains 2 phases: Estrus, or Follicular, phase: 5–7 days in length, when the mare is sexually receptive to a stallion. Estrogen is secreted by the follicle. Ovulation occurs in the final 24–48 hours of estrus. Diestrus, or Luteal, phase: 14–15 days in length, the mare is not sexually receptive to the stallion.
Foals are usually born in the spring. The estrous cycle of a mare occurs roughly every 19–22 days and occurs from early spring into autumn. Most mares enter an anestrus period during the winter and thus do not cycle in this period. [54] Foals are generally weaned from their mothers between four and six months of age. [55]
As the days shorten, most mares enter an anestrus period during the winter and thus do not cycle in this period. The reproductive cycle in a mare is controlled by the photoperiod (length of the day), the cycle first triggered when the days begin to lengthen. As the days shorten, the mare returns to the anestrus period when she is not sexually ...
This period of advertised fertility is known as oestrus, "estrus" or heat. [9] In species that experience estrus, females are generally only receptive to copulation while they are in heat [9] (dolphins are an exception). [10] In the estrous cycles of most placentals, if no fertilization takes place, the uterus reabsorbs the endometrium.
Female seasonal breeders will have one or more estrus cycles only when she is "in season" or fertile and receptive to mating. At other times of the year, they will be anestrus, or have a dearth of their sexual cycle. Unlike reproductive cyclicity, seasonality is described in both males and females.
In a harem model, the mares may "cycle" or achieve estrus more readily. Proponents of natural management also assert that mares are more likely to become pregnant in a natural herd setting. Some stallion managers keep a stallion with a mare herd year-round, others will only turn a stallion out with mares during the breeding season. [10]
Luteolysis [1] (also known as luteal regression) is the structural and functional degradation of the corpus luteum, which occurs at the end of the luteal phase of both the estrous and menstrual cycles in the absence of pregnancy.