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 compo sition and pelleting of diets fed to broiler chicks up to marketing ag e on changes in their liver size and the content and composition of li ver 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 form-diets that increase fattening-had signi ficantly (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 the se variables. Feed withdrawal for 10 or 24 h decreased, at times signi ficantly, 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 chic ks not exposed to FW was markedly affected by increases in dietary ene rgy (soybean oil) level and E:P. The main effects of the former were i ncreased levels of stearic, linoleic, and arachidonic acids and a decr eased level of oleic acid; those of the latter were an increased level of oleic and decreased levels of stearic, linoleic, and arachidonic a cids. Irrespective of the diets used, FW increased the concentrations of stearic, linoleic, and arachidonic acids, and decreased those of pa lmitic and oleic acids. This effect on arachidonic acid was consistent ly significant, whereas the effects on the other fatty acids were sign ificant in two out of three experiments. Due to these effects of EW, p art of the differences in the composition of liver fatty acids caused by dietary factors observed in fed chicks, completely disappeared afte r FW. The length of FW (10 vs 24 h) did not affect liver size or fat c ontent, 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 l iver weight and the content and composition of its fat in birds not ex posed to FW. The effects of the dietary factors on liver size and its fat content completely disappear after 24 h of FW.