The preservation of poultry gene pools, and crossing strains or breeds with respect to heterosis, reciprocal effects, selection and prediction are discussed. Published values show significant heterosis for egg production, sexual maturity, body and egg weight, and viability. Reciprocal differences are typically lower. Heterosis is due to allelic (dominance or overdominance) or non-allelic (epistasis) gene interaction. Egg production and related traits have a major epistatic component. Reciprocal differences are due to sex-linked effects (Z-chromosome genes) or maternal effects (plus w-linked genes). Sex-linked effects are generally more important than maternal effects, but maternal effects are important for early growth, and effects on viability caused by disease organisms and egg transmitted antibodies. Heterosis and reciprocal effects are influenced by age and environment. Performance across a range of environments and ages is correlated, but rankings of crosses change. In broilers, specialized sire and dam lines are used to increase effective selection pressure. In layers, within-line selection and crossing is illustrated. Data from four Leghorn strains and their crosses was used to study prediction of cross performance. For sexual maturity and body weight, expectations from pures were correlated with 2-way, 3-way and F2 means. For egg production, expectations from 2-ways were correlated with 3-way and F2 means. Predictions of 4-way means were poor.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume X. Breeding programs for swine, poultry, and fish., , 242–256, 1986
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