Estresse por calor em suínos machos castrados

Abstract

The objective was to evaluate the effects of acute and chronic heat stress on performance and physiology of pigs and to develop a fuzzy model for predicting respiratory rate and body temperature. For acute stress it was used 24 pigs housed in two climate chambers. In one of the chambers animals were in a comfortable temperature (22ºC) and in the other, in heat stress (34 °C). In each chamber were housed 12 pigs with an experimental plot represented by two animals at bay totaling six repetitions. The experiment lasted 48 hours. The environmental conditions of the chambers, respiratory rate, body and top surface temperatures were monitored on the beginning and at every four hours. There was a reduced performance in the first 24, 24 and 48 and 48 experimental hours. The animals exposed to heat had increased respiratory rate and surface temperatures. Pigs in acute heat stress showed variation in body temperature as a function of time and answered in a biphasic manner regarding acclimatization, thus compromising performance. For the study of chronic stress, 36 pigs were used for 71 days. The animals were distributed in a randomized block design, with three treatments and six replicates with two animals per experimental unit. The treatments were: HS (animals in the heat), TN (animal thermal comfort) and PFTN (animal thermal comfort pair feeding with HS). Performance data, physiological parameters, behavioral and swine carcass composition were obtained. There was a reduction in the performance of the animals subjected to heat due to intense temperature and consumption reduction. The heat promoted increased respiratory rate, surface and rectal temperatures. Restricting the consumption promoted an increase in lymphocytes. Pigs kept in HS spent more time on leisure and less time eating and digging. The heat promoted less hot carcass weight and impaired the performance, physiology and behavior of animals. The results of physiological parameters and thermographic images of acute and chronic heat stress were used for a fuzzy model. It was used as input variables: air and surface temperature and as output variables: respiration and rectal temperature. The inference method used was the Mamdani and the defuzzification technique was the center of gravity. Results of the model when compared with the experimental data showed an evident satisfactory efficiency in the determination of the respiratory rate and rectal temperature, in which the calculated R2 values were 0.997 and 0.951 for acute stress and 0.993 and 0.964 for stress chronic heat.