EVALUATION OF THE THERMAL ENVIRONMENT FOR RAISING DAIRY COWS IN A PASTURE MILK PRODUCTION SYSTEM

Abstract

The production of milk on pasture is subject to several challenges, one of them being the thermal environment to which the cows are subjected, which can be a determining factor in the quantity and quality of milk produced. Thus, the present study aimed to evaluate the thermal environment of Holstein cows, producing milk on pasture, analyzing the Temperature and Humidity Index (UTI) and the Respiratory Rate (RR).  During the experimental months, Tmax (ºC) of 40º was observed, characterizing a high value in the thermal aspect for dairy cows. As for the UTI, an average value of 72 was observed, considering the thermal environment of rearing as comfortable for the cows. During the experimental period, dairy cows were, most of the time, in conditions of mild to moderate heat stress, since the UTI and RF values observed, when compared with those in the literature consulted, suggest such a situation. However, when considering RH during the evaluation period, several peaks were observed, between 80 and 90, which warn that some days there may have been excessive humidity coinciding with a higher temperature, generating heat stress because the latent mechanisms of heat dissipation, such as sweating and evaporation, are not efficient, which can be understood by the observed RF values.  most of them are above the value considered normal, therefore RR present in the graph at high peaks of 80 to 100 mov.min-1, and this interval is classified as high heat stress. In view of the above, it is necessary to adopt strategies to mitigate the heat stress of cows, especially those with high production, since there is a direct influence between increased FR and reduced milk production.