Certain pathologic abnormalities or human influences can also cause anestrus. Then we place the stallion in a box and allow the mares to come to the stallion on their own and express estrus. Finally, we catch the mares and place a halter and lead on them and bring them to the stallion where he can tease them over a protective rail. Blanchard points out that response to teasing and intensity of estral behavior vary among individual mares. Some mares require considerable time and effort with all these methods before they show estrus, while other mares show estrus to any method used to tease them.
Some mares always show only subtle signs of estrus.
In contrast, occasional mares show intense signs of estrus with very little teasing and even occasionally show estrus to other mares, geldings, and even humans. Yet, institution of teasing the mare with a stallion often demonstrates the mare is having regular estrous cycles. This has become more of a problem with shipped semen breeding, as many of these owners are reluctant to send the mare to a breeding farm where teasing is an integral part of the breeding program. Surgical removal of the affected ovary most commonly results in the mare returning to regular estrous cycles and a fertile condition, but often not until the next breeding season. The corpus luteum is a structure that develops in the ovary on the site where an ovum is released and that secretes progesterone if fertilization occurs and pregnancy is maintained.