Uso da termografia de infravermelho e temperatura retal para avaliar a tolerância ao calor de ovinos Somalis expostos à radiação solar direta

Abstract

Animal production in the tropics is limited mainly by the heat stress imposed on animals, which causes physiological and behavioral changes. The aim of this study was to measure the surface temperatures of different regions of the body, as well as heat gain and loss, using infrared thermography, of Somali sheep subjected to heat stress and raised in a semi-humid tropical climate. Therefore, five Somali rams (12 months; 27,6 + 0,58 kg) were fed Tifton hay and concentrate (NRC, 2007), and allocated to a collective pen (56 m²). The temperature and relative humidity values were obtained in order to calculate the temperature and humidity index (ITU) as well as the solar radiation value (W/m²). The rectal and surface temperatures of points on the head, trunk and scrotum were assessed at three different times: in the shade, immediately after 60 minutes of exposure to solar radiation (from 12:00 to 13:00) and two hours after this exposure (in the shade). The thermograms obtained were analyzed using the Infrared Reporter software and areas of the eye, forehead, dewlap, ear, muzzle, neck, chest, shoulder blade, back, belly, leg, buttocks and croup were evaluated, as well as the cranial, medial and epididymal portions of the scrotum. The data was analyzed using ANOVA for repeated measures and the means were compared using the Tukey test at 5% significance. During the experimental period, the highest temperatures, THI and solar radiation were observed between 12:00h and 13:00h (40.1 °C; 90.4; 741.6 W/m², respectively), characterizing an emergency situation. As a result of the stressful conditions, rectal temperature increased by 0.6 °C with a subsequent loss of 0.4 °C after two hours in the shade. As for temperature changes in the head region, all areas showed an increase in temperature after exposure to solar radiation, with the forehead standing out with a gain of 2.6 °C. In the trunk region, the shoulder and rump showed the greatest temperature gains (3.9 and 3.6 ºC). As for the scrotum, there was an increase in temperature in the cranial region (1.6 °C) with a loss of 2.6 ºC, as well as in the medial region (1.2 ºC) with a loss of 1.9 ºC, while the epididymal region showed an increase of 1.7 ºC. However, after two hours in the shade, all regions had their temperature reduced, which was lower than pre-exposure. Therefore, it can be concluded that the use of infrared thermography was efficient in determining the heat gain and loss, especially in the head region, demonstrating the tolerance of Somali rams reared in a semi-humid tropical climate to return to their pre-exposure temperature.