Selection for Low Yolk Cholesterol in Leghorn-Type Chickens

Abstract

A study was conducted to examine the response to three generations of selection for low yolk cholesterol (milligrams cholesterol per gram yolk) in a White Leghorn Line. The phenotypic relationships of yolk cholesterol with yolk weight, egg weight, and egg production were also determined. An index selection procedure was used based, in the case of dams, on individual plus full and half-sib records, and for sires on the records of their full and half-sib sisters. Individuals that ranked lowest were selected. A randombred line was maintained. Yolk cholesterol was significantly (P<.01) lower in the selected line compared to the control line in each of the three generations. The percentage reductions in yolk cholesterol (milligrams cholesterol per gram yolk) were 2.2, 2.4, and 5.4 in Generations 1, 2, and 3, respectively. Themean heritability estimates of yolk cholesterol based on dam-daughter regression were .11 and .23 in the selected and control lines, respectively. The realized heritability estimate obtained by regressing the differences between the lines on the cumulated actual selection differentials was .26 ± .02. The correlation coefficients of yolk cholesterol with yolk weight, egg weight, and egg production were inconsistent, low in magnitude, and generally nonsignificant (P>.05) except for the negative correlation coefficients in Generation 3 with yolk weight (−.25; P<.05) in the control line and egg production (−.18 and −.27; P<.01) in the selected and control lines, respectively.