BREEDING AND GENETICS A Comparison of Combination and Family Selection in Chickens1

ABSTRACT Sire family selection was compared with index selection in six replicates of a single-generation experiment. The index comprised individual and sire family performance for rate of lay from 20 to 40 weeks of age in a synthetic White Leghorn type layer strain. Response was slightly greater to combination selection than to sire family selection, but the difference (.2%) was not statistically significant. On the basis of estimated relative efficiency value, a difference of 2.14% between selection criteria would be necessary for statistical significance, and the probability of detecting this difference in an experiment of the given magnitude would be quite low. (Key words: index selection, combination, sire family, rate of lay