Effect of time of joining and rate of stocking on the production of Corriedale ewes in southern Victoria. 2. Survival and growth of lambs

Abstract

A study of the survival and growth of lambs was made over a three year period (1968 to 1970) on a flock of 540 ewes grazing annual pasture at Werribee, Victoria. Ewes were stocked at three rates (5, 7 1/2 and 10 ha-1) and lambed between July 6 and August 20 or between September 10 and October 29 each year. Observations were made on the same ewes each year. Rate of stocking had no effect on the birth weight of lambs but single-birth lambs born in September were lighter than those born in July. More twins were born in September than in July and a smaller proportion of lambs born survived from the September than from the July lambing. Of the lambs born to ewes stocked at 10 ha-1 in 1968 and 1969 a smaller proportion survived than of the lambs born to ewes stocked at 5 ha-1. The growth rate of lambs born in July was constant between birth and weaning at 12 weeks of age but declined as rates of stocking increased. When the lambs born in September were about eight weeks old the pastures matured and growth rates of lambs declined and at weaning liveweights of lambs from plots stocked at different rates were similar. Lambs born in July on plots stocked at 5 and 79 ewes ha-1 were as much as eight kilograms heavier at weaning than the lambs born in September at equivalent rates of stocking. Neither rate nor time of onset of milk production was significantly affected by stocking rate.