Metabolic changes in broiler chickens in hot conditions : nutritional consequences

Abstract

In broiler chickens, chronic heat exposure significantly decreased basal metabolism but increased dietinduced thermogenesis when expressed as a ratio over metabolisable energy intake. The proportion of energy retention as fat was higher and as protein was lower at 32°C than at 22°C. This may result from modifications in glucose utilisation, as suspected by altered insulin secretion and/or lower tissue sensitivity to this hormone. High ambient temperature increased fatness, particularly for subcutaneous fat. The proportion of saturated fatty acids in fat tissues was higher. The increased fatness in hot conditions was not subsequent to an enhanced hepatic lipogenesis. The secretion flux of the lipoproteins VLDL or total triglycerides, which represent the capacities of lipid output from the liver to the other tissues, were not increased. Finally, the peripheral uptake of plasma triglycerides by the lipoprotein lipase in fat tissues seemed even reduced. In contrast, the mobilisation of lipids may have been lower. The reduction in protein deposition in hot conditions was mainly due to a decrease in muscle protein synthesis. It is possible that heat exposure changes the requirements of amino acids, some of them may thus be limiting factors to protein synthesis. The lower protein synthesis might also originate from a failure in the energy supply to the muscle or from changes in hormonal control. In hot conditions, although lipid upplementation was not efficient, increasing dietary protein content improved growth performance and protein retention.
This effect was favourable but relatively low.