Respostas fisiológicas e características do pelame e da pele de borregos deslanados terminados em sistema de integração lavoura-pecuária em região semiárida

Abstract

The productive performance of the lambs refers directly to the finished system, nutrition, as well as to the selected breeds and climatic factors, such as high temperatures and relative humidity, which impose pressure on the animals, resulting in a situation of heat stress. The aim of this study was to evaluate the thermoregulatory responses of Brazilian Somali and Santa Ines hair lambs finished in an crop-livestock system by monitoring the physiological, hormone and biochemical indicators, as well as the characteristics of the pelage and skin. The experiment was conducted in a semiarid region, during the finished period for 53 days. The experimental design was completely randomised with a split-plot, in-time design, including two breeds and three collection times (06:00, 14:00 and 18:00 h). The physiological variables studied were respiratory and cardiac frequency, rectal and superficial temperature, hormones triiodothyronine (T3), thyroxine (T4), cortisol and serum biochemical indicators (sodium, potassium, glucose, cholesterol, urea, total protein, albumin, globulin, albumin/globulin ratio). The variables of the pelage were the numerical density per cm2, thickness of the pelage and length of the hairs. Skin variables were thickness of the epidermis and collagen, and variables in relation to the productive performance were body weight. The microclimatic variables were monitored and the THI thermal comfort indexes were calculated. The respiratory and cardiac frequency of lambs Somalis Brasileira and Santa Inês were significantly higher (P<0.05) in the afternoon compared to morning and night. It was found that the THI influenced (P<0.05) the rectal and superficial temperature in both races, so that at 14:00 h, the values increased significantly. The responses of T3 and T4 hormones were significantly (P<0.05) higher at night and lower in the morning and afternoon. But cortisol concentrations in both races were significantly (P<0.05) higher in the afternoon. The characteristics of the pelt, skin and final body weight were similar between breeds (P>0.05). Late afternoon weather conditions made it difficult for the two races to dissipate the heat needed to maintain body temperature in a situation of thermal comfort, indicating a heat stress condition. But at night, thermoregulatory responses diminished, overcoming heat stress. The Brazilian Somali and Santa Ines hair lambs present physiological mechanisms for adaptation and morphological characteristics of the pelage and skin that allow the maintenance of homeothermia, showing adaptability to tropical conditions. Therefore, the results suggest that both breeds can be finished in an crop-livestock system with the possibility of expressing adequate productive performance.