Fatty Acid Composition of the Yolk Sac Membrane in the Chick Embryo

Background
Similar to the mammalian placenta with the chorioallantois and amnion, the avian yolk sac membrane (YSM) is comprised of the area vitellina (AVI) and area vasculosa (AVA), respectively. Understanding incorporation and delivery of nutrients (especially fatty acids) between these membranes and the developing embryo is important for improving hatchability and survival of chicks during early life. Due to its relative proximity to the yolk, we hypothesized that the AVI would be higher in fatty acid composition compared to the AVA.

Methods
Fertilized eggs from Ross broiler hens were incubated under standard conditions until embryonic day 16 (n=5) or day 19 (n=6) (hatching=day 20). To collect the YSM, the shell was cracked, albumen separated out, and the embryo within the YSM was placed into a sterile dish. The chick was then euthanized by cervical dislocation. The AVA was separated from the AVI and washed with phosphate buffered saline (PBS). The AVI was incised to facilitate removal of the yolk and washed with PBS. Membranes were separately flash frozen in liquid nitrogen. Total lipids were extracted from the AVI and AVA by the method of Folch et al.1 Fatty acid methyl esters were prepared as reported by Metcalfe et al.2 Fatty acid analysis was performed using gas chromatography as described by Cherian et al.3 Total (mean ± SD) saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA) were compared between the different membranes at each time point using one-tailed t tests. Significance was defined as P<0.05.  […]