Grzegorz Ziba 
Use of genetic variability of feed consumption in selection of laying hens

Possibility of genetic amelioration of feed conversion in laying hens parallel to continuation of improving laying rate and egg shell quality was the object of the study.
Performance results of five generations of two experimental breeds – Rhode Island Red (3997 individuals) and Sussex (3863) – were analyzed. Individual feed intake was recorded when hens were 34 and 54 weeks old. An additional selection criterion was defined as BLUP solution of feed consumption corrected for regressions on initial body weight and its change, and on the weight of eggs laid during the test. Genetic parameters of traits estimated with the use of the REML method with animal model showed values similar to those obtained in other studies. Genetic trends revealed a desired direction of changes. The initial laying rate, egg weight, shell strength and feed conversion improved.
Selection for residual feed consumption estimated with the use of phenotypic regressions, generated a correlated progress of residual feed consumption as estimated with genetic regressions. Residual feed consumption estimated with the genetic regressions is, however, a better feed consumption predictor.
An alternative, simplified selection based on feed intake recorded solely in hens from selection flocks showed moderate usefulness. Such attitude would require to periodically record the entire test flock to estimate the variances and covariances involved.
Crosses were found to lay more eggs of higher weight and stronger shells in comparison with the parental lines. Heterosis values and genetic correlations between the lines and crosses manifest compatibility of the breeds. Combined selection of lines and crosses is a better alternative to selection of only pure breeds when the improvement of the performance of crosses is the breeding aim. Inbred exerted only a slight influence on birds’ performance.
Incorporating feed consumption measurements in breeding objective has proved effective and justified.