Discounted expressions in broiler breeding programs

The commercially grown broiler usually is a crossbred from specialized purebred sire and dam lines. The position of a purebred line in the crossbreeding system influences its genetic contribution to expression of productive and reproductive performance at different stages of the production column and, thus, influences the breeding goal for a given line. In broiler breeding, cumulative discounted expressions (CDE) should be considered to define breeding goals for multitrait selection. In the present study, a systematic design for the application of discounted gene flow methodology to derive CDE for production and reproduction traits in broiler breeding was developed. Factors considered as influencing the magnitude of CDE were: crossbreeding system (two-way, three-way, and four-way cross), selection scheme (with and without progeny testing and intensity of selection), selection path, trait (production at commercial stage and reproduction at either nucleus or multiplier stage), interest rate, and time horizon for evaluation. Performance data from a commercial breeding stock were applied in the analysis. Results indicated that levels of CDE were significantly affected by all factors studied. The more that pure lines were included in the crossbreeding system, the lower the CDE for a particular selection path. However, the summation of all selection paths did not differ much among crossbreeding systems. Progeny testing decreased CDE by increasing generation intervals. The CDE for reproduction traits were higher than those for production traits mainly as a result of earlier expression of the reproduction traits.