Genetic Analysis of Chicken Egg Yolk Cholesterol

Abstract

Five yolk traits of White Leghorn eggs were analyzed for heritabilities and genetic correlations in five random bred generations and for response in two generations of selection for low mg. cholesterol/g. dry yolk. The yolk of each egg was weighed and freeze dried after which mg. cholesterol/g. dry yolk was determined. There were 40 sires mated to 600 dams in each generation for three years and 24 sires mated to 360 dams in each of the last two years. Two eggs per hen were used in the first year and the repeatabilities of wet yolk weight, dry yolk weight, yolk moisture weight, mg. cholesterol/g. dry yolk and cholesterol in total yolk were 66.1%, 66.8%, 59.5%, 80.4% and 77.0%, respectively. In the remaining generations one egg per hen was used. Pooled means of five random mated generations and heritabilities from sire variance components, dam components and regressions of daughter on dam, within sires, were: wet yolk weight, 14.52 ± 0.03 g., 0.26 ± 0.07, 0.44 ± 0.14, 0.22 ± 0.06; dry yolk weight, 7.48 ± 0.02 g., 0.24 ± 0.07, 0.48 ± 0.14, 0.21 ± 0.06; yolk moisture weight, 7.04 ± 0.02 g., 0.25 ± 0.07, 0.52 ± 0.14, 0.23 ± 0.06; mg. cholesterol/g. dry yolk, 30.36 ± 0.05 mg., 0.15 ± 0.05, negative, 0.19 ± 0.06; cholesterol in total yolk, 225.73 ± 0.66 mg., 0.27 ± 0.07, 0.10 ± 0.14, 0.28 ± 0.05. The correlations between wet yolk wt., dry yolk wt. and yolk moisture wt. were high (mostly above 0.90), while the genetic correlations between mg. cholesterol/g. dry yolk and the yolk weights were 0.28 to 0.35. There was a high 0.71 to 0.74 genetic correlation between mg. cholesterol/g. dry yolk and cholesterol in total yolk. The realized heritabilities from two replications of two generations of selection ranged from 0.04 to 0.13.