Effect of divergent selection for total plasma phosphorus on plasma and yolk very low density lipoproteins and plasma concentrations of selected hormones in laying Japanese quail

Japanese quail lines were divergently selected over 32 generations for laying hen plasma yolk precursor, as measured by total plasma phosphorus (TPP). The high (HP) and low (LP) lines were developed from a randombred control population (R1) that was maintained without conscious selection. The purpose of the present study was to characterize the composition of very low density lipoproteins (VLDL) in laying Japanese quail hens (VLDLy) and the concentration of selected hormones in laying hens from the HP, LP, and R1 lines. The changes in TPP because of genetic selection in the Japanese quail lines were associated with large alterations in plasma VLDLy concentration (HP > R1 > LP), but only minor changes in lipid composition and size (HP > LP = R1; P less than or equal to 0.01) of plasma VLDLy particles. Basal plasma levels of hormones associated with reproduction and lipid metabolism were also different among lines, with luteinizing hormone (LH) ranking HP > R1 = LP and triiodothyronine (T-3), thyroxine (T-4), and 17 beta-estradiol ranking HP > R1 > LP (P less than or equal to 0.05). The results suggest possible increased rates of hepatic lipogenesis, hepatic VLDLy assembly and secretion, and plasma VLDLy concentration in association with increases in concentrations of plasma LH, T-3, T-4, and 17 beta-estradiol. Concentrations of total lipids in yolk VLDL were not different among lines, and only minor line differences in the concentration of different classes of yolk VLDL neutral lipids were detected. The data indicate a preferential uptake of a specific plasma VLDLy subpopulation into rapidly growing ovarian follicles, resulting in a constant composition of yolk VLDL of laid eggs among lines of Japanese quail with large differences in plasma VLDLy concentration.