SALVANTE, K.G.*; WALZEM, R.L.; WILLIAMS, T.D.; Simon Fraser Univ., Burnaby, BC,Canada; Texas A&M Univ., College Station; Simon Fraser Univ., Burnaby, BC, Canada: Differential allocation of lipid resources during avian egg production

During avian egg production, hepatic lipid production increases markedly as very-low density lipoprotein (VLDL) synthesis shifts from the exclusive production of larger, generic VLDL, which transports triglyceride within an individual, to an increase in the synthesis of smaller, yolk-targeted VLDL (VLDLy), which supplies the yolk with energy-rich lipid. A nearly complete shift from generic VLDL to VLDLy has been observed in laying poultry hens. However, it was unclear whether non-poultry avian species, which have not been selected for maximum egg production, exhibit such a dramatic shift in lipid metabolism during laying. Therefore, we validated a dynamic laser scattering technique for use on a passerine bird, the Zebra Finch (Taeniopygia guttata), characterized VLDL particle diameter distribution (PDD) in laying and egg-producing Zebra Finches, examined the relationships between VLDL PDD and subsequent reproductive effort, and compared these findings to those for laying chicken hens. VLDLy particle diameter ranged from 21.5 to 51.1 nm in chickens, in comparison to 10.7 to 30.4 nm in Zebra Finches. Laying females of both species had a significantly higher proportion of VLDLy particles than non-laying females (Zebra Finch 38% vs. 4%, chicken 70% vs. 25%). The extent of inter-individual variation in VLDL PDD was more marked in laying Zebra Finches then in laying chicken hens. Furthermore, while the percentage of VLDLy was significantly related to reproductive quality in chickens (hens that laid 7 or more eggs within a 10 day period had significantly more VLDLy than hens that laid less than 7 eggs), there was no corresponding relationship in Zebra Finches (large-egg and small-egg females did not differ in percentage of VLDLy).