Hyperthermia and body energy store effects on estrous behavior, conception rate, and corpus luteum function in dairy cows.

The reproductive performance of 74 Israeli Holstein dairy cows was examined during summer. Cows were fed prepartum to reach high (3.8) and low (2.6) body condition scores by 1 mo prepartum. After calving, half of each group were cooled seven times a day for 30 min by sprinkling and ventilation. Cows were inseminated starting 60 d postpartum. Daily mean body temperatures of cooled and noncooled cows were 38.6 and 39.2 degrees C, respectively, with differences between them reaching 1 degree C and more during the hot hours. Body condition affected only the time taken postpartum to the start of ovarian activity (26 d for high and 32 d for low body condition groups). Estrous behavior lasted longer in cooled (16 h) than in noncooled (11.5 h) cows of the low body condition group only. Conception rate was higher in cooled than in noncooled cows (59 vs. 17%). Pregnancy rate at 90 d postpartum was higher in cooled (44%) than in noncooled cows (14%). Progesterone concentrations were higher in inseminated nonpregnant and in noninseminated cyclic cooled cows than in noncooled cows and were similar in pregnant cows of both cooled and non-cooled groups. The present cooling method appears to have a high potential for improvement of summer fertility.