Further investigations on the role of diet-induced thermogenesis in the regulation of feed intake in chickens: comparison of adult cockerels of lines selected for high or low residual feed intake.

The main objective of this study was to investigate the role of diet-induced thermogenesis (DIT) in feed intake regulation in cockerels selected for high (R+) or low (R-) residual feed intake. The selection criterion was defined as the difference between observed feed intake and feed intake predicted by regression between feed intake and BW, BW gain, and egg mass production. Furthermore, the effect of genotype on postprandial oxidation of U-(13)C(6)-glucose, decarboxylation of 1-(13)C(1)-Leu, and key metabolites and hormones was analyzed. Thirty 24-wk-old cockerels of both lines were kept in battery cages under standard conditions on a commercial diet. Three cockerels per genotype were examined twice weekly from wk 30 through 34 in open-circuit respiratory cells. After adaptation, cockerels were feed deprived for 24 h and heat production was measured. During the subsequent 7-h refeeding period, DIT and feed intake, as well as glucose oxidation and Leu decarboxylation were assessed by using breath tests. Blood samples were collected after fasting and refeeding. Finally, 10 animals per genotype were killed to record abdominal fat weight. Body composition of 6 different chickens per genotype was determined by using dual-energy x-ray absorptiometry. During feed deprivation, the R+ cockerels had a significantly higher heat production than their R- counterparts, which was even more pronounced during refeeding. Consequently, the R+ cockerels had a significantly increased DIT and a higher feed intake than the R- cockerels. Thus, no evidence of a feedback effect of DIT on feed intake was observed. The oxidation of U-(13)C(6)-glucose was significantly higher in the R+ cockerels, confirming their higher respiratory quotient values and the augmented fat deposition in the R- chickens, as assessed by abdominal fat weight and dual-energy x-ray absorptiometry measurements. No significant genotype effect on 1-(13)C(1)-Leu decarboxylation was observed, despite increased circulating uric acid levels in the R+ chickens. Genotype did not influence plasma levels of triglycerides, free fatty acids, glucose, triiodothyronine, or thyroxine after refeeding, whereas plasma leptin levels were significantly higher in the R+ cockerels.