Thermoregulation of Girolando cows during summertime, in Pernambuco State, Brazil
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Universidade Estadual de Maringá
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This work was carried out to evaluate the physiological thermoregulation responses of Girolandobreeddairy cows kept in feedlot during summertime. A total of 15 animals were used, belonging to three geneticgroups: 1/2, 5/8 and 3/4 Holstein-Gir (HG), with five cows from each genetic group, distributed in a completelyrandomized 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 nineweeks, 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 thermalcomfort indexes: THI (temperature-humidity index), BGHI (black globe temperature and humidity index) andRTL (radiant thermal load). 1/2 HG animals showed the highest SR and lowest RR, ET and CST of all threegenetic groups, while 3/4 HG cows had the lowest mean SR and highest ET and CST. 5/8 HG cows hadintermediate values for SR, ET and CST. Mean RR values did not differ between 5/8 and 3/4 HG cows. It wasconcluded that animals from genetic groups 3/4 and 5/8 HG showed greater sensibility to heat stress than 1/2 HGcows.
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