Reproductive and Physiological Responses of Holstein Heifers to Controlled and Natural Climatic Conditions

Abstract

Two groups (five animals each) of 12- to 15-month-old virgin Holstein heifers were used to evaluate the effects of natural and controlled hot and cool climatic conditions in a 180-day experiment on certain reproductive and physiological responses.Under cool climatic conditions (62 to 65F), the average length of the estrous cycle was 20 to 21 days, as compared with 25 and 21 days under controlled, cycled hot (75, 85, and 95F), and natural summer climatic conditions, respectively. The difference in responses under hot and cool climatic conditions was highly significant (P<0.01). Under spring, cycled hot, air conditioning, and natural summer climatic conditions the average duration of estrus was 20, 11, 20, and 14 hr, respectively. Thus, hot climatic conditions significantly (P<0.01) depressed the length of the estrual period. The incidence of clinical anestrous was 33% among the heifers during the cycled, hot period (in climatic chamber). The intensity of estrus and post-ovulatory bleeding time were decreased under hot climatic conditions.Thyroidal activity was depressed on the day of estrus in contrast to other days of the estrous cycle. Neutrophila, lymphopenia, and general leucocytosia (P<0.01) were observed on the day of estrus.