Índice de estresse térmico para ovinos nativos.

Abstract

The present study had two distinct objectives, the first of which was to estimate and quantify the levels of heat stress suffered by sheep of the Soinga, Morada Nova and Santa Inês ecotypes when subjected to different environmental conditions, in a climatic chamber. The second objective was to develop a thermal stress index for sheep, using easily measured physiological and environmental characteristics. For the first objective, eighteen animals, six of each ecotype, were distributed in a completely randomized design and submitted to eight thermal conditions (T20+AM, T20, T25, T25+FC, T30, T30+FC, T35 and T35+FC), with relative humidity between 60 and 80%. Heart rate (HR) and respiratory rate (RR), rectal (RT), skin (ST) and superficial coat (CST) temperature, respiratory rate (RR) and thermal gradient (TRTP) were calculated for each condition. evaluated thermal. The environmental data recorded were air temperature (AT), black globe temperature (BGN), relative humidity (RH), partial vapor pressure (Ea) and wind speed (V). Values of the temperature and humidity index (THI), black globe temperature and humidity index (BGHI) were calculated. The addition of AT significantly (p<0.01) affected the physiological variables of the animals. There was a difference in the physiological variables of the genotypes and, although the three groups were not well adapted to different environmental conditions and presented similar responses, the Morada Nova sheep are slightly superior, followed by the Soinga and Santa Inês sheep, respectively. For the second objective, a principal component analysis summarizes the measures of HR, RR, TR, TP and TSP in just one variable (y1). They were obtained through environmental sources and several variables, using SigmaPlot software. The equation chosen was the thermal stress index for sheep, TSI= 24.153 – (0.0523*TA) + (0.746*TGN) + (4.104*Ea), with R2

= 0.668. The correlations of the four indices (THI 1, BGHI, THI 2 and TCI), and the TSI with the physiological variables were compared. The TSI correlations with HR, RR, RT, ST and CST were 0.379, 0.686, 0.731, 0.846, 0.820 and -0.823, respectively. The values of these correlated animals were assumed as indicators of the efficiency animals' response as indicators of the animals' response. Thus, it is assumed that the TSI has a high efficiency.