Puberty and subsequent oestrous activity in young Merino ewes

Abstract

At Fowlers Gap in far western New South Wales, the exhibition of oestrus prior to 16 months of age was studied in South Australian Merino ewes born at five times of the year in three successive years. Ewes born at different times varied widely in average growth rate and in growth pattern, in response to marked changes in pastoral conditions. For different groups of ewes, considerable variation was observed in the mean liveweight at 450 days of age (34-59 kg), in mean age at puberty (283-more than 480 days), in mean liveweight at puberty (31-49 kg), and in the mean number of oestruses exhibited by 16 months of age (0-8.7). Faster growth rates were associated with both younger ages and higher liveweights at puberty. Puberty occurred at progressively younger mean ages and lower mean liveweights between December and May, suggesting an increase in environmental stimulation during that period. The age at puberty of ewes born in February and April was strongly influenced by season, growth rate being less important. Both season and growth rate influenced the performance of ewes born at other times.