The question whether commercial strains of egg-type chickens have reached a plateau or ceiling of production remains controversial. Several reports based on controlled experiments show that egg production, even after several generations of selection, contains considerable additive genetic variance and that selection has been effective (K in n ey et al., 1970; B ohren et al., 1970; Cra ig et al., 1969). On the other hand, there are some who take the point of view (for example, Clayto n, 1968) that commercial breeders during the past 2 decades or more have made little or no progress from selection. Indeed, Clayton (1972) boldly asserted that the application of quantitative genetics theory to commercial poultry production has had relatively little effect on contemporary levels of egg production.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 1, Madrid, Spain, 917–924, 1974
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