Heat tolerance of unshorn and shorn Suffolk and Ile de France ewes
Keywords:
heat tolerance index, sheep, rectal temperature, thermoregulation, woolAbstract
The objective of this study was to evaluate the heat tolerance index (HTI) in 11 Suffolk and 12 Ile de France, in the summer, in Nova Odessa (22º42'S and 47º18'W), São Paulo State, Brazil. To calculate this index the rectal temperature was registered at 1 p.m. (RT1), before they spent two hours resting in the shade. Then, they were exposed to direct sun light for an hour. After one more hour in the shade, it was registered the RT2, at 3 p.m. They stayed all this time without food and water. The HTI was calculated: 10 - (RT2 - RT1). The ewes were evaluated in sunny days, without clouds and wind, before (10, 11, 12, 13/Jan/2006) and after shearing (3, 8, 15/Feb/2006). The RT data were analyzed using the GLIMMIX procedure of the SAS software package, whereby breed, time of data sampling, shearing and interaction were modeled as fixed effects, and individual animal and date of data sampling as random effects. The same procedure as above was used to analyze the ITC, using a mathematical model that included the fixed effects of breed, and shearing in addition to the random effects of individual animal and date of data sampling, modeled with a generalized linear model. Climatic variables were taken in the moment of registering the RT and the black globe and humidity index was greater than 90 for the two times. The RT of Suffolk ewes (39.31ºC) was similar to the RT of Ile de France (39.51ºC). After shearing the RT decreased (39.60ºC to 39.23ºC, P<0.05) and the RT after heat stress (at 3 p.m.) was greater (39.49ºC, P<0,05) than before (39.34ºC). Breed or shearing not affected the HTI which is an indication that these ewes had a good heat loss, in despite of wool, and are well adapted to the hot summer in São Paulo State.
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