Lipid changes in the residual yolk and liver of the chick immediately after hatching

A study has been made of the changes in the weights, lipid and fatty acid compositions of the liver and residual yolk complex of the chick during the immediate period following hatching. By the 5th day after hatching about 85% of the gross weight and 90% of the lipid associated with the yolk complex had been absorbed. During this period, the composition of the yolk lipid displayed a marked increase in its proportion of cholesteryl esters and decreases in the triacylglycerides and phosphoglycerides. Whereas, in the triacylglycerides of the residual yolk after hatching there were changes in the proportions of the saturated fatty acids, in the phosphoglycerides there were distinctive changes in the proportions of the polyunsaturated fatty acids. Growth of the liver after hatching was associated with a substantial accumulation of fat. The very high level of cholesteryl esters associated with the embryonic liver was rapidly replaced by triacylglycerides in particular, and phosphoglycerides. The accumulation of the triacylglycerides was accompanied by a rapid change in their fatty acid composition away from that associated with embryonic development and differing markedly from that of the triacylglycerides being absorbed from the yolk. The changes in the lipid and fatty acid composition of the liver were indicative of the rapid alteration for the role of the liver in the lipid metabolism of the newly hatched chick.