Effects of different stocking intensities in early life on the productivity of Merino ewes grazed as adults at two stocking rates. 3. Survival of ewes and their lambs, and the implications for flock productivity

Abstract

A stocking rate of 20 sheep/ha in adult life was associated with greater mortality of ewes and their lambs than a stocking rate of 10 sheep/ha, but mortality was not affected by the nutrition of the ewes in early life. Survival of lambs born as twins to weaning was 42% at the high stocking rate and 72% at the low. Corresponding values for singletons were 73 and 87%. Differences in survival of singleton but not twin lambs were established during the first 5 d of life. Mortality of ewes was greater at a high stocking rate and by nine years of age approximately twice the number of ewes had died at the high as at the low stocking rate. Incisor wear and losses were greater in sheep stocked as adults at the high stocking rate, and within this flock was more marked in ewes reared at a low than in those reared at a high stocking rate. Severe wear and loss of incisor teeth were not correlated with cumulative mortality at 108 months. Data reported in this and in the two previous papers in this series were synthesized into a computer model which was used to predict wool production and the numbers of lambs and surplus ewes available for sale when culling age was varied from four to eight years. Wool production and the numbers of surplus sheep available for sale were predicted to be greater at the higher stocking rate with the exception of the number of surplus female lambs available from flocks in which their mothers were culled at six years or earlier.