EFFECTS OF HEAT STRESS ON SEXUAL BEHAVIOR IN HEIFERS

Abstract

High ambient temperatures affect the secretion of sexual hormones in cows and heifers. As a result, the frequency of silent estrus can reach a high level during summer. In order to analyze the effects of heat stress on sexual behavior in Black and White Romanian heifers, a research has been conducted on four groups of animals in the pre- and post-AI interval. During spring, in conditions of thermal comfort and under the stimulating influence of increasing photoperiod, 83.3% of the heifers showed clear signs of estrus. Exposure to temperatures of 36-42○C by day and 21-31○C by night caused anoestrus: the heifers did not respond to repeated estrus-induction treatment. When hot days (33-38○C) alternated with tolerable temperatures by night (18-21○C), a normal expression of estrus was noticed in 16.7% of the animals, while 33.3% experienced weak estrus and 50% did not exhibit sexual behavior. In conditions of moderate thermal stress, with peaks of daily temperature ranging from 28 to 34○C, clear signs of estrus were detected in 25% of the heifers and weak symptoms in 41.7%, while 33.3% had silent heat, clinically diagnosed. The circadian profile of behavior changes in heat-stressed heifers, whose sexual activity shifts to night time and to the early hours of the morning.

Keywords

• estrus behavior
• heat stress
• heifers