Özet:

In order to evaluate heat tolerance, physiological constants of 32 cows were measured (Chinampo: n = 12; Holstein: n = 10; Jersey: n = 10). From June to December 2006, rectal temperature and respiratory rate were recorded every Monday at 0600 and 1700 h. Holstein rectal temperature was affected by heat most, followed by Jersey, and Chinampo (the most heat-resistant). Respiratory rate of the 3 breeds was affected by climatic factors, but the Holstein and Jersey cows registered values higher than those of Chinampo cows. With a temperature-humidity index (THI) above 72 the physiological variables of all 3 breeds increased. The most heat accumulation during the day was registered in the dairy breeds. The difference in respiratory rate between morning and evening measurements was greater in Holstein and Jersey cows than in Chinampo cows. We conclude that Chinampo cows were the most tolerant to heat stress.

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