Sexual behavior of mares.

This research investigated the sexual behavior of mares, highlighting a normal cycle that spans three weeks and involves phases of estrus and diestrus. The study also explored social interactions between mares and stallions, discussing related hormonal changes and the role this behavior has in maintaining social structure in horse populations.

Cycling Pattern and Behavior

• The research paper explains that mares, female horses, are seasonally polyestrus. This means they typically go through multiple cycles of sexual receptivity throughout a season.
• They have an anovulatory period during the short light days of late fall and early winter and start ovulating as days become longer in winter.
• The full estrus cycle lasts about three weeks, with 5-7 days of estrus (when the mare is receptive to mating) and around two weeks of diestrus (a period of sexual disinterest).

Estrus vs. Diestrus Behavior

• The mare’s behavior changes across the estrus and diestrus phases. During estrus, a mare may repeatedly approach a stallion, urinate frequently, and stand still with hind legs spread apart. These behaviors communicate her interest in mating.
• In contrast, during diestrus, a mare avoids the stallion and may react aggressively if the stallion attempts to court her. This behavior communicates her lack of interest in mating.
• However, the researchers note that mares and stallions in long-term relationships frequently engage in non-sexual behaviors like resting, grazing, and grooming together.

Role of Hormones in Sexual Behavior

• The researchers explain that hormonal changes accompany the behavioral changes. Estradiol, a type of estrogen, initiates estrous behavior when secreted by the follicle. Progesterone, another hormone, suppresses estrous behavior when secreted by the corpus luteum (a temporary endocrine structure involved in ovulation).
• Interestingly, mares sometimes exhibit estrous behavior during anovulatory periods. The researchers suggest this could be due to estrogenic steroids released by the adrenal cortex.

Sexual Behavior’s Role in Social Structure

• Lastly, the paper suggests the mare’s year-round sexual behavior helps maintain the social structure among horses. This is unique because in most ungulates, males and females only interact during the mating season.
• In horse societies, a male typically stays with a group of females throughout the year, and the periodic display of sexual behavior by mares facilitates this social arrangement.