Management of shuttle stallions for maximum reproductive efficiency-part 2

In 1947, Burkhardt 7 reported that placing mares under lights stimulated follicular development and onset of estrus. He also postulated that the T M stimulus probably passed through the eyes. Another 30 years would lapse before investigators at Colorado State University would report that gradually increasing photoperiod on stallions resuited in changes in seminal characteristics, sexual behavior and hormonal concentrations in blood serum. 44.4s It is interesting to note that although the stallion represents 50% of the breeding herd, research on factors affecting his fertility have been sorely neglected in relation to the mare. There are five primary factors responsible for "normal" fertility in the stallion. They are: age, season, testicular size, frequency of ejaculation and sexual behavior. 3a The physiological aspects of these factors are interrelated, and dramatically influenced by circulating levels of hormones that are highly responsive to the ratio of light to dark.