Size and components of poult yolk sacs.

An experiment was designed to examine the effects of strain of turkey, size of egg, and stage of embryonic development on yolk and yolk sac utilization. Sixty eggs from Nicholas and British United Turkeys of America (BUTA) breeders were selected within each of the weight categories 70 to 76, 80 to 86, and 90 to 96 g. These eggs were incubated under commercial conditions, and eggs selected at 0 or 25 d incubation, at hatch, and 24 h posthatch and yolk and embryos were weighed and assayed for fat, protein, or fatty acids. Yolk weight declined from 23.7 g at setting to 4.66 g at hatch and subsequently to 2.87 g, 24 h posthatch. Yolk weight was affected by strain and egg weight and a number of significant (P < 0.05) interactions were observed. Nicholas strain birds yielded the largest yolks, with the strain difference being most pronounced for the largest egg weight category. Larger turkey eggs contained more water, such that at 24 h posthatch there was double the amount of residual water in the yolk sac. At 24 h posthatch, the Nicholas poults had more water available in the residual yolk. Egg weight had little effect on lipid reserve in the yolk or yolk sac after 25 d incubation. Fatty acid profile of yolk lipids changed little throughout incubation. A number of strain differences are seen in fatty acid profile in the yolk during utilization, although these are quite small and may not be of sufficient magnitude to account for any strain differences seen in early poult viability or growth. Data suggests that the poult and chick may be different in metabolism of various lipid fractions, although in general nutrient utilization by the poult follows a fairly well established sequence of events.