Reproductive Physiology of the Stallion. VIII. Artificial Photoperiod, Collection Interval and Seminal Characteristics, Sexual behavior and Concntrations of LH and Testosterone in Serum1

Abstract

Stallions were subjected to a gradually increasing photoperiod beginning on October 15, 1973. The maximum artificial daylength (16 hr) was imposed on February 8, 1974, and maintained until October 6, 1974. Two ejaculates were collected from each of five treated and four control stallions weekly, with an interval of 24 hr between die paired ejaculates on the first and alternate weeks, and an interval of 1 hr on the second and alternate weeks. During summer, stallions subjected to the artificial photoperiod produced less (P<.05) gel-free semen and gel per ejaculate and had more (P<.05) spermatozoa per ml of gel-free semen than untreated stallions. Consistent differences due to artificial photoperiod were not observed for spermatozoa per ejaculate or percentage of motile spermatozoa. Light treatment did not affect mounts per ejaculate or seminal pH, but stimulation time was reduced (P<.05) in treated stallions during late winter. Mean concentration of LH in the serum of untreated stallions varied (P<.01) over time and appeared to be highly seasonal. A corresponding change in concentration of testosterone was not observed (P<.05). Mean concentrations of both LH and testosterone were greater (P<.05) in the serum of treated stallions than in untreated stallions during winter. Means for first and second ejaculates for the 1-hr interval differed (P<.01) for all characteristics except motility. Means for first and second ejaculates for the 24-hr interval differed (P<.01) for all characteristics except motility and mounts per ejaculate. Collection interval did not affect characteristics of first ejaculates (P>.05), but second ejaculates differed (P<.05) for all characteristics except motility. Copyright © 1977. American Society of Animal Science . Copyright 1977 by American Society of Animal Science.