Inbreeding Effects Contrary to the Direction of Selection in a Poultry Flock

REPORTS of the adverse effects of inbreeding on production traits of poultry are numerous (see Jull, 1933, for early references, and Stephenson et al., 1953, for more recent investigations). None of them, however, appear directly to consider the particular problem of the effects of inbreeding on egg-production in a flock specifically selected for this character, and in which the computed coefficients of inbreeding rise only because of the limited size of the population. A study of these effects in such a flock might yield information pertinent to the cessation of gains after long-continued selection and, more generally, to the future of closed flock breeding. The University of California Single Comb White Leghorn flock selected for egg-production seems to be particularly suited for a study of this issue. Its history has been given in some detail by Lerner (1950), and need not be restated here. It should, however, be stressed that …