Efficiency of selection in layer-type chickens by using supplementary information on feed consumption : I. Selection index theory.

Selection indexes to maximize net income for egg laying chickens were constructed with information on egg mass output, body weight and individual feed records. Relative selection efficiencies were then compared with different kinds of information in the index. If the genetic variation in feed consumption is completely determined by egg mass output (M) and body weight (W), using reliable estimates of genetic correlations or pehnotypic regressions of these traits with feed consumption in the index is equally efficient to an index with individual feed records. If real genetic differences in feed efficiency exist which are independent of egg mass and body weight, (h u (2) ), then there is greater justification in using individual feed consumption records. Forexample, if h u (2) =0.2, h W (2) =0.6, h M (2) =0.15 and rGWM (genetic correlation)=0.2, the use of individual feed records is expected to improve efficiency of the selection for net income by 9 p. On the other hand, if the genetic correlations of feed consumption on body weight and on egg mass are substituted in the index for records on individual feed consumption, only slightly less selection efficiency would result.