Efeito do ambiente térmico nas respostas fisiológicas, produtivas, características do pelame e no comportamento de vacas holandesas puras por cruza no norte de Minas Gerais

Abstract

The objective was to evaluate the influence of climatic conditions in northern Minas Gerais on the physiological and productive in Holstein cows by pure crosses, in lactation. The experiment was conducted in two phases, July / August and October / November 2010 using 12 lactating females, totaling 18 days of assessments in each phase. Physiological parameters such as respiratory rate (RR), rectal temperature (RT) and coat surface temperature (CST) and the production were observed in the morning and afternoon during the three days of the week. The rate of sweating was measured once a week totaling six samples in each phase. Climatic data such as temperature (DBT), relative humidity (RH), dew point temperature (Tpo) were collected by a datalogger, as the black globe temperature (BGT) was measured with a black globe thermometer, these variables were collected inside and outside the place where the animals were housed. Physiological variables showed clear seasonal pattern, with higher values during the warmer months and lower during the colder months. Even with thermal comfort index above 80, there was no evidence of stressful values for rectal temperature, respiratory rate and temperature of the coat, but there was a reduction in milk production in the warmer months. Although an effect of the experimental phase on the parameters studied, these remained within the normal range for lactating Holstein cows.