Efeitos da hora e do mês nos indicadores fisiológicos de estresse térmico de novilhas mestiças leiteiras

Abstract

Weather conditions can influence the productive performance and welfare of dairy cattle. Behavior in the thermal environment, especially with regard to thermophysiological variables, are important indicators of welfare and, consequently, in the growth and performance of dairy heifers. The objective was to study the interference of meteorological conditions of the coldest and hottest months and the time of day on the thermoregulation of crossbred dairy heifers raised in the Brazilian Cerrado. Data was collected in the Glória Experimental Farm in the dairy cattle sector of the Federal University of Uberlândia (UFU) located in Uberlândia, Minas Gerais, Brazil. The temperatures rectal (RT), forehead (FT) and respiratory rate (RR) of 11 crossbred dairy heifers were measured in the hottest months (October, November and December) and in the coldest months (June and July) in the morning and in the afternoon. The temperatures of the environment and of the globe and the humidity of the air were measured at the same time as the physiological measurements. The temperature and humidity index (THI), the equivalent temperature index (ETI) and the radiant thermal load (RTL) were calculated. The heifers showed statistically lower values of RT, FT and RR in the morning (38.39ºC; 29.14 mov.min-1 ; 27.35ºC, respectively) than in the afternoon (38.70ºC; 34.13 mov.min-1 and 32.25ºC, respectively). These variables in the coldest months (38.40ºC; 28.63 mov.min-1 and 27.83ºC) were statistically lower in the warmer months (38.69ºC; 34.63 mov.min-1 and 31.77ºC). The time of day and the coldest and hottest months influence the thermophysiological variables of crossbred dairy heifers reared in a tropical environment