Egg production, body weight and egg quality characters; their heritability and the correlations between them

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Abstract
The heritabilities of and genetic correlations between part record production, body weight, egg weight, shell colour, specific gravity and albumen quality have been estimated in one strain each of Light Sussex and Rhode Island Red and in three strains of White Leghorns using variance and covariance components in a hierarchical classification. The heritability values are in general agreement with published figures. Because of the wide variation in the size of the variance components no valid conclusions about the effects of sex linkage, dominance or maternal effects can be drawn from this type of analysis. Significant positive genetic correlations exist between: egg weight and body weight in four strains; egg weight and shell colour in one strain; body weight and Haugh units in one strain; specific gravity and Haugh units in one strain, and a negative correlation exists between body weight and shell colour in one strain. Because of the difference in genetic correlations, selection is thought likely to have a rather different outcome on the characters in each strain and stress is laid on the need to calculate genetic parameters separately for each strain.