Plasma apolipoprotein VLDL-II and egg production in laying hens: establishment of an ELISA method.

The developmental pattern of apolipoprotein VLDL-II (apo-II) in the plasma with regard to lipid concentration was characterized during the transition of pullet females to the laying phase in commercial laying hens (Gallus domesticus). Apo-II was isolated from the plasma of estrogen-administered roosters, and a rapid ELISA was developed for its quantification in chickens. The sensitivity of the assay was 5 ng/ml, and the inter- and intra-assay coefficients of variation were 4 and 8%, respectively. Whereas no detectable levels of apo-II could be monitored in the blood plasma of immature chickens, the level increased slightly to 23 weeks of age and sharply at the onset of lay. This profile reflects the dramatic changes in lipid metabolism at the onset of lay, and concurs with the concentration of total lipids in the plasma and with egg production rate. Plasma apo-II of 2 laying strains differing in body weights but compared at approximately similar egg production rates, tended to be slightly higher in heavy vs light-weight type hens. Oogenesis was speculated to be the main factor affecting both apo-II and total lipid profiles in chicken plasma, enabling efficient delivery of VLDL to the egg.