The survival of lambs in shelter declines at high stocking intensities

This experiment evaluated the effect of stocking intensity at lambing on lamb survival. A randomised block design with three replicates compared stocking rates of 16 and 30 ewes/ha. Twin-bearing Merino ewes (n = 69) that had been mated with Poll Dorset x White Suffolk rams were placed in paddocks sheltered with rows of hessian, with 8 or 15 ewes per 0.5-ha plot for the low and high stocking rates, respectively. The survival of lambs born alive at the high stocking rate (63%) was 24% less (P = 0.002) than for those at the low stocking rate (83%), and was associated with a higher (P < 0.05) proportion of lambs dying from starvation, mismothering or exposure. There were no differences (P > 0.05) in lamb birthweight, marking weight, ewe liveweight or condition, suggesting nutritional conditions between the stocking rates were similar. The results suggest caution in using lambing strategies which require high stocking rates.