Poult yolk sac amount and composition upon placement: effect of breeder age, egg weight, sex, and subsequent change with feeding or fasting.

Hatching eggs from 48 and 55-week-old Small White turkey breeders were used to examine the yolk sac of these poults. Influences due to flock age, egg weight, poult sex, and a two day postplacement regimen of feeding or fasting were evaluated in a factorially designed experiment. Each variable was found to act independent of the other. Older breeders gave eggs having a greater percentage yolk and with more ether extract than if they were from younger hens. For the most part, these fundamental differences remained with the poult's yolk sac at and after placement. Examining egg weight effects apart from hen age showed that heavier eggs had heavier yolks but their percentage of the total was to the converse and no compositional differences appeared. Poults from large eggs had a greater amount of yolk sac that contained proportionately less ether extract than if they were from small eggs. In total, yolk sac found ca. 12 h after poult removal from the hatcher corresponded to reserves that would remain ca. two days after formal hatching. The yolk sac free carcass failed to exhibit any compositional differences regardless of egg source or weight upon placement, but 48 hr later changes occurred that could largely be attributed to interim yolk resorption. Fasting delayed yolk sac uptake and favored removal of moisture and lipid to a greater extent than protein while the converse was true if access to feed and water was permitted. All parameters were unaltered because of poult sex.