1. The responses to genetic selection on yolk proportion as a technique for increasing egg dry matter content, an important criterion for the egg-product industry, was investigated in a pedigree flock of White Leghorn hens.2. Parents were preselected on high and low yolk proportion from a base population. The absolute estimated breeding value for yolk proportion of both groups differed by 3%. The realised selection difference in dry matter content of eggs between groups was more than 1% in the analysed offspring population.3. Heritability estimates were moderate and dry matter had a lower heritability (h(2)=0.39) than yolk proportion (h(2)=0.44).4. The genetic correlation between yolk proportion and dry matter content was highly positive (r(g) =0.91). Genetic correlations with egg weight were negative and would have to be compensated for in a breeding programme (r(g)=-0.76 with yolk proportion and r(g)=-0.64 with dry matter content). The genetic correlation between the laying performance and yolk proportion was r(g)=0.28 and close to zero (r(g)=-0.05) for dry matter content.5. Easy recording and lower undesirable correlations make yolk proportion more suitable for commercial selection compared with egg dry matter content in layer breeding
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