Reproductive wastage in Merino sheep in semi-arid tropical Queensland : Observations on flock mated during the spring and summer

Abstract

Observations on Merino flocks mated during the late spring and summer in semi-arid tropical Queensland indicated that reproductive wastage was due mainly to failure to lamb ; such failure was due both to anoestrus and the failure of oestrous ewes to conceive. Nevertheless, in the five groups of mature ewes observed, lamb marking percentages ranged from 63.4 to 75.0. In a group of ewes mated when 17 months old, lamb marking percentage was only 38.9. The level of oestrous activity appeared to be influenced by the time of lambing previous to mating, and in some cases a relatively high level of oestrous activity (>90 per cent in 28 days) was observed during the spring months. Conception rates were observed to be satisfactory during the spring (>70 per cent.), but deteriorated during the summer. Neonatal mortality rates were low (approximately 10 per cent) due to favourable climatic and pastoral conditions at the time of lambing and the most important cause of mortality was predation by the wedge-tailed eagle (Aquila audax) and raven (Corvus coronoides).