Intra-Flock Genetic Merit under Floor and Cage Managements

THE increasing use of individual cages for laying birds raises a number of problems of significance to breeders. Among them is the question of the relative efficiency of selection for cage performance on the basis of floor records and vice-versa. The problem may be viewed as an example of the general situation in which the efficiency of direct selection for a trait is compared with the efficiency of another criterion of selection. Whatever may be the difference in heritabilities of the two traits, gains in one can be influenced by selection with respect to the other only if the genetic correlation between the two traits is different from zero. The usual estimates of this correlation are well known to be subject to extremely large sampling fluctuations. Nor, in the absence of knowledge of the distribution of these estimates, can one make a significance test whether its value is equal to …