Thermoregulation of Girolando cows during summertime, in Pernambuco State, Brazil/Termorregulacao de vacas da raca Girolando no periodo de verao, no Estado de Pernambuco, Brasil

This work was carried out to evaluate the physiological thermoregulation responses of Girolandobreed dairy cows kept in feedlot during summertime. A total of 15 animals were used, belonging to three genetic groups: 1/2, 5/8 and 3/4 Holstein-Gir (HG), with five cows from each genetic group, distributed in a completely randomized design, in subplots. The physiological parameters were sweat rate (SR), respiratory rate (RR), epidermis temperature (ET) and coat surface temperature (CST), and were evaluated once a week, during nine weeks, from December 2009 to February 2010, totaling 135 observations. Throughout the experimental period, climatic data were recorded using an automated weather station, and later used to calculate the different thermal comfort indexes: THI (temperature- humidity index), BGHI (black globe temperature and humidity index) and RTL (radiant thermal load). 1/2 HG animals showed the highest SR and lowest RR, ET and CST of all three genetic groups, while 3/4 HG cows had the lowest mean SR and highest ET and CST. 5/8 HG cows had intermediate values for SR, ET and CST. Mean RR values did not differ between 5/8 and 3/4 HG cows. It was concluded that animals from genetic groups 3/4 and 5/8 HG showed greater sensibility to heat stress than 1/2 HG cows. Keywords: dairy cattle raising, heat stress, physiological parameters. Este trabalho foi realizado com o objetivo de avaliar as respostas fisiologicas de termorregulacao de vacas leiteiras da raca Girolando, no periodo de verao, mantidas em confinamento. Foram utilizados 15 animais de tres grupos geneticos: 1/2, 5/8 e 3/4 Holandes-Gir (HG), sendo 05 vacas de cada grupo genetico, distribuidas num delineamento inteiramente casualizado, em parcelas subdivididas. Os parametros fisiologicos: taxa de sudacao (Tsud), frequencia respiratoria (FR), temperatura da epiderme (TE) e temperatura de superficie de pelame (TSP) dos animais foram avaliados uma vez por semana, durante nove semanas, de dezembro de 2009 a fevereiro de 2010, totalizando 135 observacoes. Durante todo o periodo experimental os dados climaticos foram registrados atraves de uma estacao meteorologica automatica, e usados posteriormente para calcular os indices de conforto termico: ITU (indice de temperatura e umidade), ITGU (indice de temperatura de globo e umidade) e CTR (carga termica radiante). Os animais 1/2 HG apresentaram Tsud mais alta e FR, TE e TSP mais baixas nos tres grupos geneticos, enquanto nas vacas 3/4 HG foram verificadas a