Review of Canadian, Outaouais and Rideau Arcott breeds of sheep

Estimation of genetic parameters and selection response for reproductive and growth traits in Rideau-Arcott sheep

The goal of this study was to estimate genetic parameters and predict direct and correlated response to selection for lamb growth traits and ewe reproductive traits, based on single-trait selection or combining multiple traits in an optimum index that targets total litter post-weaning weight in the first lambing as the main selection goal. Heritability estimates ranged from 0.04 to 0.19. Genetic correlations between growth and reproductive traits ranged from −0.24 to 0.15. The indirect response to selection for reproductive traits in later lambings, by selecting on first lambing performance, was 11%–25% greater than direct selection. The response to indirect selection for composite reproductive traits, i.e., total weaning weight or total post-weaning weight, by selecting on individual lamb weaning weight or post-weaning weight was 1%–69% greater than direct selection, but it was accompanied by a negative response on litter size. However, combining alternate growth and reproductive traits in optimum selection index resulted in correlated response of up to 96% greater than direct selection response for reproductive traits without a negative response on litter size. Therefore, multiple trait selection using an index of component traits was more effective than direct selection for a composite trait.

[Prediction of retained heterosis and evaluation on breeding effects of composite livestock populations]

A composite population is a breed made up of two or more component breeds and designed to benefit from hybrid vigor without crossing with other breeds, and is thus regarded as an alternative method for heterosis utilization. The breeding effects depend on retained heterosis in livestock composites. This paper reviews prediction methods of retained heterosis, relative production efficiency and production performance, and evaluation methods of breeding effects of composite populations. A composite population contains all three types of heterosis. If inbreeding can be avoided, it can retain heterosis to a certain extent. The retained heterosis depends on the number of contributing breeds and their proportions in the composite. The production performance rests both on average breeding values of contributing breeds and on retained heterosis of the composite itself. Breeding effects of composite population can be evaluated by theoretical prediction, actual estimation of retained heterosis, examination of genetic variation and/or comparison with other relevant breeds.