Resumen de Heat tolerance in naturalised cattle in Brazil: physical factors

H. Louvandini, G.R. Paludo, A. A. Egito, J.A.S. García, C. McManus, A. S. Mariante

• The objective of this study was to evaluate the heat resistance in different breeds of naturalised cattle, at two different times of day with different temperatures and humidity. The experiment took place at Sucupira farm of Embrapa/Cenargen in Brasília-DF. A total of 52 animals were used, 11 Curraleiro, 11 Crioulo Lageano, eight Nelore, eight Pantaneiro, six Junqueira, four Holstein and four Mocho Nacional including both males and females. The measurements were taken at 08:00 and 14:00 after the animals had been exposed to the sun for 6 hours. The procedure was repeated 3 times. The data collected included heart rate (HR), rectal temperature (RT) and respiratory rate (RR). Blood was also collected as well as sweating rate and the length and number of hairs per cm2. Breed influenced (p<0.001) the heat response. The Nelore breed had the best response (HR= 66.06, RR= 32.71, RT= 39.36 and sweating= 215.22), followed by the Junqueira (HR= 76.71 RR= 33.05 RT= 38.75 Sweating= 247.14), which although had high heart rate maintained the other parameters at a low level. The Pantaneira presented the lowest variation between morning and afternoon measurements (HR= -1.61, RR= -0.28, RT= +0.19, Sweating= +20.65). The Mocho Nacional and Holstein were the least adapted with high means (Mocho Nacional: HR= 71.44, RR= 42.38, RT= 39.25, Sweating= 323.22; Holstein: HR= 69.34, RR= 39.57, RT= 39.37, Sweating= 269.13). The Holstein had a greater number of hairs per cm2 although its sweating rate was not the highest. The results enable the differentiation between breeds with higher and lower heat resistance in the conditions of the experiment.