Interrelationship between the effects of dietary factors and feed withdrawal on the content and composition of liver fat in broiler chicks.

Four experiments were carried out to evaluate the effects of the composition and pelleting of diets fed to broiler chicks up to marketing age on changes in their liver size and the content and composition of liver fat due to feed withdrawal (FW) during 0, 10, and 24 h. Birds not exposed to FW that were fed diets with high energy to protein ratio (E:P) and diets in pelleted from-diets that increase fattening-had significantly (P < 0.05) higher liver fat content than those fed diets with the recommended E:P and in mash form, respectively. Those fed pellets also had higher liver weight. Dietary energy level did not affect these variables. Feed withdrawal for 10 or 24 h decreased, at times significantly, liver weight and its fat content, irrespective of the diets fed previously. The values observed after FW were not affected by the dietary factors evaluated. The composition of liver fatty acid in chicks not exposed to FW was markedly affected by increases in dietary energy (soybean oil) level and E:P. The main effects of the former were increased levels of stearic, linoleic, and arachidonic acids and a decreased level of oleic acid; those of the latter were an increased level of oleic and decreased levels of stearic, linoleic, and arachidonic acids. Irrespective of the diets used, FW increased the concentrations of stearic, linoleic, and arachidonic acids, and decreased those of palmitic and oleic acids. This effect on arachidonic acid was consistently significant, whereas the effects on the other fatty acids were significant in two out of three experiments. Due to these effects of FW, part of the differences in the composition of liver fatty acids caused by dietary factors observed in fed chicks, completely disappeared after FW. The length of FW (10 vs 24 h) did not affect liver size or fat content, but the concentrations of oleic and arachidonic acids in liver fat were significantly higher in birds exposed to 24 h of FW. It was concluded that the composition and form of the diets markedly affect liver weight and the content and composition of its fat in birds not exposed to FW. The effects of the dietary factors on liver size and its fat content completely disappear after 24 h of FW.