IMPROVEMENT OF MERINO REPRODUCTIVE PERFORMANCE THROUGH BLOODLINE SUBSTITUTION AND CROSSING

SUMMARY The size and relative influence of direct and maternal components of bloodline effects and average heterosis on fertility, litter size, lamb survival and net reproduction rate of Merinos were examined to assess the opportunity for improvement of Merino reproductive performance through bloodline substitution and crossing. Data on more than 8500 ewes from a Merino bloodline crossing experiment were analysed. Direct bloodline effects influenced significantly litter size only, whereas maternal bloodline significantly affected litter size, lamb survival and net reproduction rate. Direct heterosis was a significant influence on fertility and net reproduction rate, with crossbred matings being 4% more fertile and having 7% more lambs per ewe mated. Significant maternal heterosis for litter size, lamb survival and net reproduction rate indicated that crossbred dams had larger litters (3%) and higher lamb survival (7%) and weaned more lambs per ewe mated (8%). Reproductive performance of Merino flocks can be improved by both between bloodline selection and structured crossing systems