Abstract

Ultrasonic scanning for pregnancy diagnosis in commercial sheep flocks has highlighted the magnitude of lamb loss from scanning to docking or weaning. From seven ram breeding flocks in Landcorp Farming Limited, lamb survival rates were derived from the number of lambs per ewe present at six stages: pregnancy scanning, birth, born alive, 48h after birth, end of lambing and weaning. Differences in lamb survival rates between adjacent stages provided the mortality rates for five intervals: pregnancy scanning-birth; birth-born alive; born alive-48h after birth; 48h after birth-end of lambing; end of lambing-weaning. Flock-year affected lamb survival rate at all stages (P<0.001) but varied with ewe age and lamb birth/rearing rank (P<0.001). Mean lamb survival rates for 3- and 4-year-old dams were generally higher than those of other dam age groups. Triplet-reared lambs had consistently lower survival rates than single- or twin-reared lambs (P<0.001). Lamb mortality rates for the five intervals were 0.03, 0.08, 0.03, 0.03 and 0.04 lambs per potential lamb at scanning, respectively. Lamb mortality was highest at birth, with lower survival rate of triplet-born lambs compared with single- and twin-born lambs (0.82±0.006 vs 0.93±0.004 and 0.93±0.002 lambs per potential lamb respectively; P<0.001). The results indicated when, and to what extent, lamb losses occurred in the field between pregnancy scanning and weaning, and the importance of applying appropriate ewe/lamb feeding and management policies to minimise lamb mortality rates.

GB, Nicoll, KG Dodds, and MJ Alderton

Proceedings of the New Zealand Society of Animal Production, Volume 59, , 98-100, 1999