Effects of sire, sex and type of birth and rearing on follicle shut down in merino sheep

Abstract

We examined the incidence of follicle shut down in progeny of 14 different sires in a Central Test Sire Evaluation Scheme, one month after the break of the season in South Australia. On average 1.4 % (range 0 to 21 %) of follicles were classified as 'shut down' and there was no significant effect of sire or sex on shut down incidence, nor was there any relationship between fibre diameter or clean fleece weight and follicle shut down. Single born and reared sheep had a higher incidence of shut down follicles than those born as twins or raised as twins (p<0.0001). It appears that there is no genetic basis to follicle shut down and therefore little opportunity to select for genotypes resistant to the environmental effects on follicle activity.