Effect of environmental temperature on performance and on physiological and hormonal parameters of gilts fed at different levels of digestible energy

Forty crossbreed gilts were kept in an environment of thermal comfort (22.7 1.568C) and another 40 in a heat stress environment (31.7 1.408C), with average initial weights of 15.2 0.87 and 15.3 1.14 kg, respectively. The aim of the trial was to evaluate the influence of environmental temperature on performance, accretion rates of carcass protein and fat and physiological and hormonal parameters. Experimental diets containing five levels of digestible energy (13.40, 14.03, 14.65, 15.28 and 15.91 MJ DE feed kgÿ1) were supplied ad libitum until the end of the experiment, when the animals reached the average weight of 30.0 1.88 and 29.5 1.72 kg in the thermal comfort and heat stress environments, respectively. The weight gain and the intake of the diet, protein and energy by the gilts kept in a 328C environment were, respectively, 8.78, 8.22, 8.12, and 8.32% lower (P < 0.01) than those of gilts kept in a 228C environment. The environmental temperature did not influence (P > 0.05) feed : gain ratio, conversion ratio and the efficiency of protein and energy utilization. The gilts kept under heat stress showed greater (P < 0.01) ratios of fasting weight/live weight and carcass weight/fasting weight. However, their fat deposition rate was 12.8% less (P < 0.01), while that of protein did not change (P > 0.10) in relation to those animals kept in thermal comfort. Environmental temperature influenced (P < 0.01) the absolute and relative weights of all organs evaluated, gilts kept thermal comfort having heavier organs. The serum blood concentrations of the thyroid hormones, tri-iodothyronine and thyroxine, were reduced (P < 0.01) at the high temperature. No difference was observed in the rectal temperature of gilts kept in the two environments. However, the respiratory rate of the animals under heat stress rose (P < 0.01) by 36.1%. Despite lesser weight gain as well as protein and energy intake, the physiological and hormonal adjustments of the animals kept at a high temperature allowed them to maintain their efficiency of protein and energy utilization, the protein deposition rate at values Animal Feed Science and Technology