GENETIC CORRELATION AND HERITABILITIES FOR PUREBRED AND CROSSBRED PERFORMANCE IN POULTRY EGG-PRODUCTION TRAITS

Genetic correlations between purebred and crossbred performance and purebred and crossbred heritabilities were estimated for egg production traits of laying chickens using a multivariate sire model accounting for additive relationships between sires, Two sire lines, denoted lines 1 and 2, were crossed to one dam line to produce crossbred progeny. Records for egg weight, egg specific gravity, and egg number were collected on purebred and crossbred hens. In total, 99 sires in line 1 and 292 sires in line 2 were used in the analysis, each sire producing on average 45 purebred and 105 crossbred daughters. Estimates of purebred heritability in Lines 1 and 2 were in range of .54 to .74 for egg number traits, .52 to .91 for egg weight traits, and .41 to .83 for egg specific gravity traits. Estimates of crossbred heritability were .04 to .51 for egg numbers, .23 to .45 for egg weight, and .13 to .31 for egg specific gravity. The sire component in crossbreds differed up to 78% from the sire component in purebreds depending on traits. The estimate of genetic correlation (Lpc) between purebred and crossbred performance was .56 to .73 for egg number, .69 to .99 for egg weight, and .72 to .82 for egg specific gravity. Although crossbred parameters were strongly affected by environmental factors, the results tend to agree with the theory that traits with a larger dominance variation and a larger difference between sire components in purebreds and crossbreds show a lower r(pc). Because the estimates of r(pc), were significantly lower than 2 for egg number and egg specific gravity, an optimal selection strategy should combine purebred and crossbred information for crossbred progress.