One-generation divergent selection on large and small yolk proportions in a White Leghorn line

1. A striking change in egg consumption from shell eggs toward egg products is taking place. Consequently, internal egg quality traits must be seen in a different light, as they may affect the profitability of the egg process ing industry. In order to study the possibility of using breeding as a mean s to alter yolk production, a one-generation divergent selection experiment was set up. The trait was yolk proportion. The effect of hen's age on egg composition was also studied. Genetic parameters for yolk proportion, yolk weight, egg weight and albumen weight were estimated, using a multiple trai t animal model, and restricted maximum likelihood. 2. Selection response was obtained for yolk proportion and correlated selec tion responses for yolk weight and albumen weight. In the 'high line' a dec rease in egg weight and an increase in yolk weight was established, whereas in the 'low line', egg weight remained more or less the zsame and yolk wei ght decreased slightly 3. Yolk proportion, yolk weight, egg weight and albumen weight all increase d with increasing age of the hen in both selection lines. The difference be tween selection lines in yolk proportion, yolk weight and albumen weight pe rsisted throughout the laying period. 4. Estimated heritabilities for yolk proportion, yolk weight, egg weight an d albumen weight were 0.38, 0.22, 0.34 and 0.41 respectively. The genetic c orrelation between yolk proportion and yolk weight was 0.52, whereas the ge netic correlations with egg weight and albumen weight were -0.51 and -0.74 respectively. 5. We conclude that selection can be used to alter yolk production. Selecti on can be at an early age with a sustained effect throughout the laying per iod.