The effect of litter size and sward height on ewe and lamb performance

This study compared ewe and lamb performance in twin- and triplet-bearing/rearing ewes offered varying sward heights from day 64 (P64) of pregnancy until weaning at day 87 (L87) of lactation. Ninety-six twin- and 90 triplet-bearing Romney ewes were randomly assigned on P64 to four replicated sward height treatments (2, 4, 6, and 8 cm sward height). Within 24-36 h of parturition (L1) the ewes were reassigned to two (4 and 8 cm) replicated sward heights until weaning at L87. Ewes grazing the 2 cm sward height during pregnancy were significantly (P < 0.01) lighter at P99 and P132 and at L1 than ewes grazing 4, 6 or 8 cm swards. These ewes also had significantly (P < 0.01) lower dry matter intakes, condition scores, and ultrasonic backfat depths. Litter size had no effect on ewe intake, ewe liveweight or condition score throughout pregnancy and lactation. Ewes grazing the 2 cm sward height had significantly (P < 0.05) lower dry matter intakes during pregnancy than ewes on the 4, 6. and 8 cm treatments. Estimated herbage dry matter intakes measured using n-alkanes were similar to calculated energy requirements. Lambs born to ewes grazing the 2 cm swards during pregnancy were lightest at birth (P < 0.01), but sward height during C pregnancy or lactation had no effect on lamb weaning weight or lamb survival rate to weaning. Triplet-born lambs were 0.9 kg lighter (P < 0.05) than twins at birth, with the difference increasing in those lambs reared as a full triplet set to 4.7 kg at L87. Lamb losses were 14% in twin-born lambs and 32% in triplet-born lambs. There was no sward height by litter size interaction for ewe liveweight, intake or lamb birth and weaning weight or survival, therefore the results suggest ewes rearing either twins or triplets should be fed sward height allowances of 4 cm or better during pregnancy. However, there is no need to feed above 4 cm in pregnancy or lactation to optimise lamb weaning weight, lamb survival or ewe liveweight and condition score gain.