Energy utilization by the broiler chicken as affected by various fats and fat levels.
Two experiments were designed to investigate the effects of fat supplementation at different levels on energy utilization by the broiler chicken. In one experiment, finisher diets containing 2.5, 5.0, or 10.0% of added corn oil (CO), poultry oil (PO), tallow (T), or a commercial hydrolyzed animal-vegetable fat blend (HB) were fed. In the second experiment, starter diets containing 0, 2.5, or 7.5% added CO, PO or HB were fed. Metabolizable energy (ME) values were not controlled through formulation but were determined experimentally. Energy retention was measured by a slaughter technique, and metabolic energy losses were calculated as the difference between metabolizable energy intake and energy deposition in the carcass. Broilers that were fed PO, T, and HB failed to adjust feed intake to control caloric intake. They ate significantly more ME calories per day when these fat sources were fed, gained more, were fatter, and had a lower feed:gain ratio than broilers fed no added fat or lower levels of fat. Failure to regulate caloric intake when fats are added to diets may be a component of the "extra caloric" effect of fat. Broilers which were fed CO tended to regulate their caloric intake better than those which are fed PO, T, and HB. It was not determined if CO is less palatable than the other fat sources or if the unsaturated fatty acids metabolically regulate appetite. When CO was fed, broilers tended to have lower feed:gain ratios than when the other fats were fed. There was an indication that daily heat production was less when CO was fed, which would suggest a lower heat increment. Fatty acid analysis verified the efficient use of dietary fats for adipose deposition and suggested a disproportionately greater use of the unsaturated fatty acids for carcass lipids.