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.

Efficiency of selection in layer-type chickens by using supplementary information on feed consumption : II. Application to net income.

The value of individual feed consumption records to improve net income through genetic gain was investigated in an egg-type breeding operation. Genetic and phenotype parameters were estimated for body weight, egg mass and feed consumption on 788 layers from two pure lines and 1120 reciprocal crosses. Individual feed records were obtained on all birds over an 8-week test period and on 303 birds over a 24-week period. From the parameter estimates, selection indexes with and without feed consumption records were compared. Also, in lieu of feed records, selection indexes were constructed, which included genetic correlations and phenotypic regressions involving feed records. Although the heritability estimate for the efficiency of feed consumption, independent of body size and egg size, could not be accurately estimated because of the limited amount of data, the results showed that the addition of feed consumption records increased the efficiency of the selection index by 9 % .