Effects on lifetime reproductive performance of phenotypic selection for fleece weight, fibre diameter, body weight and related selection indexes: II. Selection group x environment interaction

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 south west Queensland. There were no significant effects on lifetime reproduction rate or on any of the component traits, of selection for fleece weight, fibre diameter or either of the two selection indexes. Selection for body weight had a significant positive effect on lifetime litter size (p<0.001) and an almost significant positive effect on lifetime reproduction rate (p=0.060). Despite the substantial range in yearly mean reproduction rate (0.69 to 1.01), 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 do not support the view that selection for increased fleece weight may adversely affect lifetime reproduction rate.