Preliminary Results of Bidirectional Selection for Yolk Cholesterol Level in Laying Hens

Egg yolk cholesterol was measured on a total of 67 hens from a closed population of White Leghorns. Three eggs per hen were analysed to arrive at the mean cholesterol level for each hen. Milligrams percent of egg yolk cholesterol was determined for each egg according to the method described by Abell (1952). This method was modified by using the color reagent of Zlatkis et al. (1953). Egg yolk cholesterol level ranged from a low of 921.4 mgs.% to a high of 1755.6 mgs.% with the parental population mean being 1268.8 mgs.%. A significant negative correlation was observed between rate of production and egg yolk cholesterol level with a significant positive correlation between hatch of fertile eggs and egg yolk cholesterol. Rate of production and hatchability accounted for approximately 16% of the variance in egg yolk cholesterol. Eight-tenths of a standard deviation on each side of the population mean was used to truncate this population into low, medium and high egg yolk cholesterol dams, and to establish selection intensities. Egg yolk cholesterol level was determined on a random sample of 137 progency from the parent dams. A highly significant difference of 71.45 mgs.% of cholesterol was found between the mean egg yolk cholesterol level of the progency from the low cholesterol dams and the progeny produced from the high cholesterol dams, indicating separation of the populations after one generation of selection. The heritability of yolk cholesterol level based on intrasire regression of offspring on dam was 0.24.