Partitioning genetic variance in composite sheep

Abstract

Australian sheep producers have been moving towards an increased use of composite crossbred ewes to achieve higher performance and greater genetic gain, taking advantage of the high value lamb market. Sheep research has traditionally been carried out on purebred flocks or their first and second crosses with replication and uniformity of breed types within the data. Within composite lines, the breed combinations are often complex, with multiple breeds in variable proportions with few sheep per breed combination. To enable estimation of between and within breed genetic effects, the analysis performed in our study included both additive and dominance genetic effects at the breed level. Breed additive effects contributed to 1.3% of the variation in weight. The variance associated with breed dominance effects were significant for both weight and height (10 and 5%). Results from this analysis on the small sub set are promising, and suggest the model will account for breed effects when a larger composite sheep data set is analysed.