RESUMO
The purpose of this study was to understand and discuss the relationships of the thermal environment, morphophysiological response, performance, and carcass traits of Brahman bulls from weaning at 18 months exposed to grazing conditions based on the physiological and evolutionary rationale behind the different proposals for the thermal adaptation of zebu cattle. Fifty-three uncastrated and clinically healthy bulls with birth and weaning weight of 34.0 ± 3.32 kg and 215.5 ± 44.75 kg, respectively, were evaluated. Fifteen canonical correlations were estimated, but only six were significant: thermal environment × thermoregulatory responses (rc = 0.4635; P = 0.0413); thermal environment × performance (rc = 0.4338; P = 0.0218); thermoregulatory responses × performance (rc = 0.5119; P = 0.0071); hair coat characteristics × performance (rc = 0.4939; P = 0.0273); hormone × carcass traits (rc = 0.5408; P = 0.0698); and performance × carcass traits (rc = 0.9644; P < 0.0001). Thermal environment, thermoregulatory responses and hair coat morphology influence of 18.81%, 21.49% and 24.40%, respectively, were found in the performance. We also concluded that (i) rectal temperature (RT) is a homoeothermic indicator; (ii) sweating rate (SR) is an important heat dissipation mechanism to explain the adaptation of zebu animals in the tropics and is related to weight at 550 days (W550); (iii) coat morphology, especially length (HL), diameter (HD) and hair density (ND) are related to animal performance; and (iv) hormonal profile, mainly T4, influences the carcass traits (yield, weight, subcutaneous fat and marble meat).
Assuntos
Bovinos , Pelo Animal , Criação de Animais Domésticos , Animais , Regulação da Temperatura Corporal , Brasil , Bovinos/anatomia & histologia , Bovinos/sangue , Bovinos/fisiologia , Hidrocortisona/sangue , Masculino , Temperatura , Tiroxina/sangue , Tri-Iodotironina/sangue , Clima TropicalRESUMO
The purpose of this study was to evaluate the relationship between adaptive and productive performance and determine which characteristics related to adaptation could be included as criteria for the selection of Brahman bulls managed in a tropical region. Fifty Brahman bulls were evaluated in relation to productive performance and adaptive capacity to a hot environment. The animals were grouped according to the following characteristics: Respiratory rate (RR), Sweating rate (SR) and coat traits. Three clusters were formed with these different characteristics related to thermoregulation after that these clusters were compared with productive performance that includes weighing of animals, carcass and scrotal circumference. The high adapted group corresponded to the animals with higher productive performance, with heavier animals in terms of weight at 550 days and carcass weight. The principal components analysis (PCA1) showed that carcass weight (0.95), weight at 550 days (0.92) and gain weight (0.71) were characteristics strongly correlated with the performance of the animals. These sets of characteristics were analyzed together (productive characteristics) in a multiple regression. The animals with better productive performance presented shorter hair, a greater capacity to heat dissipate by sweating and a lower rectal temperature. These characteristics were most suitable to inclusion in the breeding programs, resulting in higher economic gains. It is possible to simultaneously select resistant animals to thermal stress as well as to maintain the productivity of the flocks.