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Causes of Low Breeding Efficiency in Dairy Cattle Associated with Seasonal High Temperatures¹

Department of Dairy Science, University of Arizona, Tucson

ABSTRACT

Evidence is presented which indicates that a low rate of fertilization and a high rate of embryonic mortality are the major factors causing the low seasonal breeding efficiency associated with high ambient temperature and humidity in lactating dairy cows. Changes in environmental temperature and humidity affecting breeding results correspond closely to the time of breeding, indicating that this is probably the critical period that fertility is affected.

There was no evidence that nonfertile services associated with the high climatic temperature had any influence on the success of subsequent services.

Not only were there more long estrous cycles (those exceeding 26 days) following nonfertile service during the months of high ambient temperatures, but the prolonged cycles were significantly longer than those occurring during the other months.

¹ Contribution from Arizona Agricultural Experiment Station, Technical Paper No. 728.

² Graduate student.

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