Current Flock Effects on Lifetime Reproductive Performance of Simulated Selection at 102 Hogget Age in Merino Sheep, for Fleece Weight, Fibre Diameter, Body Weight and Relevant Selection Indexes: III. High rainfall region results

The effects of simulated selection at hogget age for fleece weight, fibre diameter, body weight and two relevant selection indexes on lifetime fertility, litter size, lamb survival and reproduction rate have been examined for a medium-wool random breeding flock of Merino sheep grazing in the New England tablelands of NSW. Simulated single trait selection for increased fleece weight, fibre diameter, and body weight had significant positive effects on lifetime fertility (P<0.05; P<0.01; P<0.01 respectively), litter size (P<0.001; P<0.001; P<0.001 respectively) and reproduction rate (P<0.001; P<0.001; P<0.001 respectively)). There were no significant effects on lifetime reproduction rate or on any of the component traits, of simulated selection for either of the two selection indexes. Despite the substantial range in yearly mean reproduction rate (0.55 to 1.09), the selection group x lambing year effect was not significant for any combination of the reproduction and production traits and there was no tendency for the selection group differences in reproduction rate to increase or decrease over the observed range in mean reproduction rate. These data reinforce the findings from earlier papers in this series and do not support the view that selection for increased fleece weight may adversely affect lifetime reproduction rate.