a1 Department of Poultry Science, The Pennsylvania State University, University Park, PA 16802-3501USA
In laying hens, cholesterol is primarily biosynthesized in the liver and incorporated into vitellogenin (VTG) and triglyceride-rich very low density lipoprotein (VLDL) particles, which are secreted into the bloodstream and subsequently taken up by growing oocytes via receptor-mediated endocytosis. VLDL and VTG are then intracellularly transformed into yolk, constituting 60% and 24% of yolk dry matter and 95% and 5% of yolk cholesterol, respectively. During the past four decades, research efforts directed toward reducing shell egg cholesterol content have centred on genetic selection or alteration of the laying hens’ diet with various nutrients, natural products, non-nutritive factors, or pharmacological agents. The present paper will provide a justification for low-cholesterol egg production, primarily in the context of the heterogeneity of response to dietary cholesterol in humans, and will review cholesterol metabolism in the laying hen, avian embryonic cholesterol needs, and genetic and nutritional approaches to chicken egg cholesterol reduction. A subsequent paper will provide a comprehensive overview of the use of non-nutritive dietary factors and select pharmaceuticals as egg cholesterol-lowering agents, and will discuss emerging strategies for lowering the cholesterol content of shell eggs.
(Received January 09 2006)
(Accepted July 13 2006)
Presented in part at the 3rd International Symposium on Egg Nutrition for Health Promotion, April 18-21, 2004, Banff, Alberta, Canada