Submitted to: International Congress for Breeding and Genetic Improvement of Beef
Publication Type: Proceedings
Publication Acceptance Date: November 10, 1997
Publication Date: N/A
Technical Abstract: High levels of heterosis were observed for growth rate, reproduction, and maternal traits including milk production. Generally, retained heterosis in advanced generations was equal to, or greater than, expectation based on retained heterozygosity in the three composite populations. Results suggest that specific cross heterosis is of some importance. Use of aver- age values for F1 heterosis and of retained heterosis based on genetic expectation in advanced generations of inter se mated composite populations is suggested for Bos taurus breeds. These results, generally, support the hypothesis that heterosis in cattle can be accounted for by dominance effects of genes. Thus, heterosis in breed crosses involving Bos taurus breeds can likely be accounted for as recovery of accumulated inbreeding depression that has occurred in breeds since their formation. Estimates of genetic standard deviations and phenotypic coefficients of variation were similar for parental purebreds combined and for composite populations combined for most bioeconomic traits. Estimates of heritability were similar for parental purebreds and composites. Thus, no increase in genetic variation was observed in composite populations relative to contri- buting purebreeds. Composite populations (breeds) have a high degree of uniformity both within and between generations. Composite populations (breeds) offer an alternative breeding system that is generally competitive with crossbreeding for using heterosis and is easier to manage regardless of size of herd. Composite populations (breeds) offer a procedure that is more effective than continuous crossbreeding for using genetic differences among breeds to achieve and maintain optimum performance levels for major bioeconomic traits on a continuing basis.