Effect of pre-weaning farm environment on adult wool production of Merino sheep

Abstract

The influence of pre-weaning environment on the adult productivity of medium Peppin Merino sheep has been examined in field experiments. In 1983 and 1984 groups of pregnant ewes and. subsequently, their lambs were run with breeding flocks on farms located over the Central Tablelands and Central Western Slopes of New South Wales. After weaning, each year's progeny grazed as a single flock at Condobolin on the Central Western Slopes, thus allowing the sheep equal nutritional opportunity in post-weaning and adult life. Differences in the progeny's liveweight and wool production could be attributed to the effects of the different environmental conditions experienced before they were weaned. Birth weight and lamb growth rates were affected (P<0.001) by early environment. At weaning, mean group liveweights covered a range of 6.9 kg in 1983 and 7.8 kg in 1984. In both years the proportion of the phenotypic variation of liveweight due to pre-weaning environment fell from approximately 0.35 at weaning to 0.15 (P<0.001) at 12 months of age, but the proportion was not significantly different from zero when the progeny were 24 and 36 months of age. Pre-weaning environment affected the production of greasy wool (P<0.001) over the progeny's first year of life. However, among the 1983 progeny no differences in wool production were observed at 24 and 36 months of age. With 1984 progeny no differences occurred at 24 months of age or, when the wool weights were adjusted to a common liveweight by covariance, at 36 months of age. Yield, fibre diameter and staple length were not affected by pie-weaning environment when measured at 24 and 36 months, and there were no differences between groups in the ratio of secondary to primary wool follicles or in wool follicle density at 36 months of age. It is concluded that the adult productivity of Merino sheep is unlikely to be permanently reduced by poor pre-weaning environmental conditions on farms but overall flock productivity will be reduced if fewer weaners survive.