OVERFEEDING INCREASES VERY-LOW-DENSITY LIPOPROTEIN DIAMETER AND CAUSES THE APPEARANCE OF A UNIQUE LIPOPROTEIN PARTICLE IN ASSOCIATION WITH FAILED YOLK DEPOSITION

Structurally specific very low density lipoprotein (VLDL) particles are presumed to redirect VLDL uptake during yolk deposition. Egg production is an energy intensive process, but energy excess negatively affects egg production. This study sought to determine whether overfeeding changed hen lipoprotein profiles, and if so, whether changes were related to egg production. Overfeeding caused 33% of hens to stop yolk deposition and reabsorb unovulated follicles (involute). VLDL of control hens possessed characteristic small particle size (30 nm) and composition indicative of limited intravascular metabolism. Overfeeding generally increased VLDL diameter, the effect being slight (+6.6 nm) in overfed laying hens when compared to overfed-involuted hens (+51.2 nm), Changes in composition indicated that increased intravascular metabolism of VLDL parallelled increases in particle diameter. Overfed-involuted hens showed significant elevations of plasma low density lipoprotein, VLDL cholesteryl ester, and high density lipoprotein (HDL) triacylglycerol content. Overfeeding increased plasma HDL, and in association with involution, caused redistribution of HDL particle sizes, including the appearance of novel HDL similar to 20 nm in diameter, termed HDL(R), and a 97 kDa protein within the HDL fraction. The overfed hen model may provide new insight into the role of lipoprotein physical properties in determining the metabolism of triacylglycerol-rich lipoprotein, and the process of reverse lipid transport. jlr Overfeeding generally increases VLDL size and plasma HDL levels suggesting that increased peripheral metabolism, and perhaps mechanical exclusion of enlarged VLDL by the granulosa basal lamina, contribute to the obesity and impaired yolk deposition observed in hens with excessive energy intakes. Temporal definition of massive VLDL enlargement relative to follicular collapse remains to be established. Cessation of yolk deposition accompanied by reabsorption of partially developed follicles appears to be associated with specific redistributions of HDL subpopulations and appearance of HDL(R).