Diallel cross of six long-term selected leghorn strains with emphasis on heterosis and reciprocal effects.

Six strains under long-term selection for egg production and other economically-important traits were crossed in a full diallel, and tested with two commercial stocks and two control strains at two stocking rates (1 bird per 20.3-cm cage and 3 birds per 30.5-cm cage) and two diets (with and without an oyster shell supplement). The mean of the 30 strain crosses exceeded the mean of the six selected strains for egg production and egg quality traits, sexual maturity and viability, which in turn exceeded the performance of both of the control strains. The performance of several of the 30 strain crosses was similar to the commercial stocks. The only significant genotype X environment interaction was for Haugh units at 450 d. Performance at the lower stocking rate was generally superior to that at the higher stocking rate. General combining ability was important for the complete array of traits measured. Specific combining ability was important for the majority of traits. Heterosis was important for all traits except specific gravity, Haugh units, blood spots and laying house viability to 272 or 496 d at the higher stocking rate. The magnitude of heterotic effects was generally greater at the higher stocking rate. Reciprocal effects were important for egg production traits, sexual maturity, egg quality traits and viability. The dietary oyster shell supplement resulted in an improvement in shell quality as measured by specific gravity.