Group selection for adaptation to multiple-hen cages: selection program and direct responses.

A selection experiment was initiated with a synthetic line of White Leghorns in 1982 to improve adaptability and well-being of layers in large multiple-bird cages by use of a selection procedure termed "group selection". With this procedure, each sire family was housed as a group in a multiple-bird cage and selected or rejected as a group. An unselected control, with approximately the same number of breeders as the selected line, was maintained for comparison and housed in one-third cages. Annual percentage mortality of the selected line in multiple-bird cages decreased from 68% in Generation (G)2 to 8.8% in G6. Percentage mortality in G6 of the selected line in multiple-bird cages was similar to that of the unselected control in one-bird cages (9.1%). Annual days survival improved from 169 to 348 d, eggs per hen per day (EHD) from 52 to 68%, eggs per hen housed from 91 to 237 eggs, and egg mass (EM) from 5.1 to 13.4 kg, whereas annual egg weight remained unchanged. The dramatic improvement in livability demonstrates that adaptability and well-being of these birds were improved by group selection. The similar survival of the selected line in multiple-bird cages and the control in one-bird cages suggests that break-trimming of the selected line would not further reduce mortalities, which implies that group selection may have eliminated the need to beak-trim. Corresponding improvements in EHD and EM demonstrate that such changes can also be profitable. The most surprising finding was the rate of which such improvement took place, with the majority of change in survival occurring by the third generation. However, EHD continued to improve at the rate of 4% per generation.