Abstract:The present study was designed to investigate the effect of chronic heat exposure (32° constant) on plasma metabolites and hormone concentrations in broiler chickens. At 2 and 4 weeks of age, fifty-four male Shaver broiler chickens were allocated to one of three treatments: 22°ad lib. feeding (22AL), 32°ad lib. feeding (32AL) and 22°,pair-feeding with the 32AL group (22PF). Ambient temperature was kept constant at either 22 or 32° for 2 weeks. Plasma glucose, triacylglycerols, phospholipids, non-esterified fatty acids (NEFA), individual amino acids, uric acid, insulin, triiodothyronine (T3), thyroxine, corticosterone were determined. Sensitivity to exogenous insulin was also measured at 7 weeks of age. At 4 and 6 weeks of age, i.e. after 2 weeks at high ambient temperature, fasted 32AL chickens displayed similar concentrations of glucose and triacylglycerols to those of 22AL birds. When fed, 32AL chickens exhibited higher plasma levels of glucose and decreased concentrations of NEFAand amino acids. Feed restriction resulted in intermediate values. Concentrations of all plasmafree amino acids were decreased under heat exposure except for aspartic acid, glutamic acid andphenylalanine. At 6 weeks of age, plasma T3 was reduced irrespective of the nutritional state, while plasma corticosterone concentrations were increased in 32AL birds compared with 22AL birds. Heat exposure did not change plasma insulin concentration in either fasted or fed chickens. The 32AL chickens displayed significantly reduced sensitivity to exogenous insulin when fasted,but an enhanced response to insulin when fed, compared with both 22° groups. Such endocrinological changes could stimulate lipid accumulation through increasedde novolipogenesis, reduced lipolysis and enhanced amino acid catabolism under chronic heat exposure.
Metabolic and endocrine changes induced by chronic heatexposure in broiler chickens : biological and endocrinological variables
