Cholesterol Metabolism in the Laying Hen as Influenced by Dietary Cholesterol, Caloric Intake, and Genotype

Three trials, each with 24 hens, were conducted to determine the effects of dietary cholesterol, caloric intake, and genotype on the synthesis, storage, and excretion of cholesterol in the laying hen. The two genotypes of birds used in this experiment had been divergently selected for high and low oxygen consumption and had been shown to differ significantly (P<.01) in body weight gain and carcass lipid deposition from 0 to 4 weeks of age. The dietary treatment, administered for a 2-week period to birds in each genotype, consisted of two levels of dietary cholesterol (0 and 1% added) and two energy intakes (ad libitum and 75% ad libitum). The experimental design was a 2 × 2 × 2 factorial. One percent added cholesterol versus none supplemented produced a significant (P<.01) decrease in available metabolizable energy and uptake of acetate into liver cholesterol while causing significant (P<.01) increases in egg and liver cholesterol but not in plasma cholesterol. Restricting caloric intake, as compared to ad libitum feeding, resulted in significantly (P<.01) decreased egg production and total amount of cholesterol excreted via the egg with significantly (P<.05) increased plasma and liver cholesterol levels but no change in egg cholesterol concentration. Differences were significant (P<.05) between the two genotypes in feed intake and hepatic cholesterol and lipid synthesis. The results suggest that: 1) a minimum level of cholesterol is maintained in the egg that is not decreased by egg production, energy intake, or genotype; 2) cholesterol levels in the hen result from a balance of dietary intake, biosynthesis, and excretion of cholesterol and cholesterol by-products; 3) cholesterol and lipid synthesis can be changed by selection for oxygen consumption, which theoretically alters metabolic rate.