Effect of season and high environmental temperature on fertility of Holstein cattle.

The breeding records and meteorological data for cows with first services between July 1, 1979, and June 30, 1980, in a large Florida herd were analyzed to determine the relationship between temperature and breeding efficiency. Seasonal high environmental temperatures were associated with low breeding efficiency. Increased maximum temperature from 29.7 degrees C during April to 33.9 degrees C during July was associated with a decrease in conception rate on first service from 25 to 7%. Also, the average number of inseminations per conception, based on pregnancy diagnosis 6 to 8 wk after breeding, was higher from May to August (4.5 to 5.3) than from September to April (2.3 to 3.5). Days open were longer for the cows first inseminated during May, June, and July (173, 171, and 167 days, respectively) than during other months (99 to 149 days). Temperature decreases of any magnitude for 1 to 3 days before or after the day of breeding, when maximum temperatures on the day of breeding were greater than or equal to 27 degrees C, were associated with higher pregnancy rates. Also, similar temperature decreases around the time of breeding, below the previously mentioned high maximum temperatures for 20 days before the day of breeding, were accompanied by higher conception rates. Fertility was consistently lower under all temperature changes when maximum temperatures on the day of breeding were greater than or equal to 33 degrees C.