Cross-breeding performance of white Leghorn and Australorp lines selected under continuous light for short interval between eggs: full-year egg production and efficiency of food utilisation.

White Leghorn (LS) and Australorp (AS) lines selected for short oviposition interval and their control lines (LC and AC), together with three strains of Australian commercial layers, were evaluated for crossbreeding performance. The estimates of selection effect on crossbreeding performance in lines LS and AS respectively were 3.5% and 15.2% for survivors' egg number, -3.3% and -2.0% for average egg weight, and 4.3% and 7.4% for efficiency of food utilisation. Compared to the commercial strains, the LS X AS cross was 13 to 15% higher for egg number, 7 to 10% lower for egg weight and 2 to 7% better for efficiency of food utilisation. The LC X AC cross laid more but smaller eggs than the commercial strains. This raised the question of how effective conventional selection in the commercial nucleus flocks had been in improving egg number in the previous 10 years, a period when the control lines had been bred without deliberate selection.