peer-reviewedA 4-year study was undertaken to evaluate the effects of two contrasting management
systems [year-round grazing (YRG) and normal seasonal grazing followed by indoor
feeding during winter (GWF)] on performance of mid-season lambing ewes. On the
GWF system, the annual stocking rate was 14.4 ewes/ha, grass silage was conserved
for winter feeding indoors, and the ewes were lambed indoors and were then turned
out to pasture. The YRG system was stocked at 10.5 ewes/ha, was grazed during the
winter, had outdoor lambing and the animals had access to all the farmlet for summer
grazing. The ewes were Belclare and Cheviot × Belclare which were balanced
across systems. Mean lambing dates and fertiliser N application rates were 20 and 30
March, and 85 and 92 kg/ha, for the GWF and YRG systems, respectively. Concentrate
supplementation during late pregnancy was similar on both systems. For the GWF and
YRG systems, litter size, lamb mortality, number of lambs reared, birth weight (kg),
weaning weight (kg) and lamb carcass output (kg/ha) were 2.17 and 2.24 (s.e. 0.038),
10.1 and 13.8% (P = 0.05), 1.77 and 1.78 (s.e. 0.042), 4.0 and 4.7 (s.e. 0.05, P < 0.001),
27.9 and 30.8 (s.e. 0.25, P < 0.001) and 469 and 348, respectively. Belclare ewes had a
higher litter size (2.34 v 2.07; s.e. 0.038, P < 0.001) and number of lambs reared per
ewe joined (1.86 v 1.69; s.e. 0.048, P < 0.01) than the Cheviot × Belclare ewes. There
were no significant interactions between system and ewe breed type. It is concluded that
the YRG system of prime lamb production was sustainable using prolific ewes but at
a reduced stocking rate (−26%) and with greater lamb mortality relative to the GWF
system. Ewe genotypes with a mean litter size of up to 2.34 lambs are suitable for both
systems. Lamb carcass output of 501 kg/ha was achieved from a primarily grass-based
system of mid-season prime lamb production using prolific ewes (Belclare)
