Thermal comfort zoning and its impact on dairy production in Rio Grande do Sul state, Southern Brazil

Thermal comfort is one of the main factors that influence the productivity of dairy cattle. The temperature-humidity index (THI) is one of the most used indicators to evaluate thermal comfort levels. This work aimed to evaluate the levels of thermal comfort for bovine dairy production in Rio Grande do Sul state through the THI calculation and its impact on milk production, considering daily yields of 15 kg and 30 kg per cow. The THI values and decrease in milk yield were calculated using data between 1990 and 2021 from the National Institute of Meteorology (INMET). The observed results considering the average temperatures showed that conditions of thermal discomfort occur only in summer, intensifying in January. Milk production was most affected in the western border region of the state, corresponding in parts to the physiographic regions of Alto Uruguai, Missões, and Campanha, which have a warmer climate. The climate classification proposed by Maluf had the best spatial correspondence with the ITU. This classification may be used in the evaluation of places with greater suitability for dairy farming in the state and to indicate places where it is necessary to implement action to mitigate the effects of thermal discomfort in dairy cattle.