Efficiency of one- and two-stage selection indexes for improvement of net economic merit in White Leghorns

The effects of varying intensities of selection at first and second stages, for a given final intensity, on the efficiency of two-stage index selection are described. Data collected on four White Leghorn strains for part and residual egg number, body weights at 20 and 40 weeks and egg weight at 39 to 40 weeks were utilised. Four of the five traits were used in the first stage and all five traits were used in the second stage for the construction of two-stage selection indexes. The index that utilised all five traits had the maximum efficiency for one-stage selection. The relative efficiency of the two-stage index increased with increase in proportion selected at the first stage. A practical breeding schedule that adds the advantage of reduced generation interval by utilising a two-stage index selection is suggested for egg type chickens.