Onset, duration and intensity of behavioral estrus were determined by evaluation of mare’s responses to a teasing stallion. In the presence of the stallion, typically diestrous mare showed no signs of receptivity, walked away from the stallion or expressed some aggression as striking, kicking,squealing, etc. At the beginning and at the end of estrus, a mare showed some interest to the “teasing” stallion including approach of the male, some winking of the vulva and
tail-raising but at the end she most often walked away from the stallion. In Fig. 2, those periods are represented by gray color. At estrus when “teased” with the stallion, the mare lifted her tail to the side, frequently urinated by viscous urine, turned hindquarters toward the stallion and lowered a rump with continuous “winking” of the vulva. In Fig. 2,the periods of estrus are represented by a darker gray color.