Changes in the lipid metabolism of the chick embryo with parental age.

A study has been made on the distribution and composition of the lipids associated with the yolk contents, yolk sac membrane, liver, and extrahepatic tissues of chick embryos at Days 15 and 19 of incubation from 25- and 41-week-old broiler-breeder stock. The higher embryo mortality displayed by the eggs from the young breeders was associated with an abnormal distribution of lipid between the tissue pools. The amount of lipid associated with the total yolk, i.e., yolk contents plus yolk sac membrane, of the embryos from the 25-week-old parents at Day 19 of incubation was greater than that of the embryos from the 41-week-old parents, and there was a much higher proportion of lipid still remaining in association with the yolk contents. In the embryos from the young parents, a smaller proportion of embryonic lipid was associated with the extra-hepatic tissues at Day 19 of incubation. Differences were observed in the relative proportions of the major lipid fractions within the yolk and embryonic tissues between the eggs from the two sets of parents. The higher mortality of the embryos from the young parents was associated with a malfunction of yolk lipid assimilation and mobilization from the yolk contents thereby denying access to the major nutrient associated with development during the last week of incubation.