Environmental influences on the postpartum animal.

Environmental influences on postpartum reproduction of the ewe, cow and sow are quite evident. Photoperiod predominantly controls the reproductive cycle of ewes lambing in the spring season and presents little problem in ewes lambing in the fall. The effect of hot ambient temperature and high humidity on ewes bred during anestrus and those bred after estrous cycles resume (late summer) needs study. In the southern regions of the United States hot ambient temperature and high humidity severely impair postpartum reproduction in cattle of European breeding. In the postpartum postweaned sow from southern states such as Minnesota, a marked reduction in reproduction during late summer and early fall has been reported. Presently, the physiological mechanisms by which hot ambient temperature and high humidity influence postpartum reproduction are not fully understood in the ewe and cow, and even less so in the sow. Hot temperatures and high humidity at the time of breeding of the ewe and cow reduce conception rates and subsequent pregnancy rates. Ewes and cows exposed to hot temperatures have increased rectal and uterine temperatures that may cause lower pregnancy rates. Altered hormonal levels and uterine blood flow have been associated with increased environmental, rectal and uterine temperatures.