Effects on lifetime reproductive performance of phenotypic selection for fleece weight, fibre diameter, body weight and related selection indexes

Abstract

The effects of simulated selection at hogget age for fleece weight, fibre diameter, body weight and two relevant selection indexes on lifetime fertility (EL/EJ), litter size (LB/EL), lamb survival LW/LB) and reproduction rate (LW/EJ) has been examined for a medium-wool random breeding control flock of Merino sheep grazing in south west Queensland. There were no significant effects on lifetime reproduction rate or any of the three 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=0.059). These data do not support the view that phenotypic selection for increased fleece weight will have adverse effects on lifetime reproduction rate.