Effect of Season and High Environmental Temperature on Fertility of Holstein Cattle

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Abstract
The breeding records and meterologic data for cows with 1st services between July 1, 1979-June 30, 1980, in a large Florida [USA] herd were analyzed to determine the relationship between temperature and breeding efficiency. Seasonal high environmental temperatures were asociated with low breeding efficiency. Increased maximum temperature from 29.7.degree. C during April to 33.9.degree. C during July was associated with a decrease in conception rate on 1st service from 25 to 7%. Also, the average number of insemination/ conception, based on pregnancy diagnosis 6-8 wk after breeding, was higher from May-Aug. (4.5-5.3) than from Sept.-April (2.3-3.5). Days open were longer for the cows 1st inseminated during May, June and July (173, 171 and 167 days, respectively) than during other months (99-149 days). Temperature decreases of any magnitude for 1-3 days before or after the day of breeding, when maximum temperatures on the day of breeding were .gtoreq. 27.degree. C, were associated with higher pregnancy rates. Also, similar temperature decreases aroung 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 .gtoreq. 33.degree. C.