Assessment of contrasting perennial ryegrasses, with and without clover, under continuous sheep stocking in the uplands. 4. Animal performance in years 4–6

Relative sheep production from Aurora (very early flowering), Mellra (late-flowering tetraploid) and Aberystwyth S23 (late flowering) perennial ryegrass ( Lolium perenne L.) varieties was compared during harvest years 4-6 (1988-90) as grass only (200 kg N ha⁻¹) and grass/clover (75 kg N ha ⁻¹ in 1988, 0 kg N ha⁻¹ in 1989 and 1990) at Bronydd Mawr Research Centre (310-363 m) in mid-Wales. The pastures were continuously stocked with Beulah Speckled Face ewes and their Suffolk cross lambs from spring to mid-July. From late July to early November only the weaned lambs grazed the swards.
Mean (1988-90) total annual lamb production per hectare from Aurora and Meltra was 70% and 16% more than that from S23. However, the difference between both varieties and S23 was much greater as grass/clover (Aberystwyth S184 small-leaved type) than as grass-only swards. Differences between the grasses in individual lamb growth rates were most pronounced during the post-weaning period, when that on Meltra was 38% and 23% more than on Aurora and S23 respectively.
Mean annual lamb output from grass/clover swards was only 70% of that from grass-only swards during the 2 years when the former swards received no fertilizer N. Averaged over the 3 years (1988-90) individual lamb liveweight gain post weaning was 38% higher on grass/clover than on grass-only swards.
The results are discussed in relation to those for the first 3 harvest years (1985-87). It is concluded that, although Aurora was less persistent than both late-flowering varieties, its superiority in providing an average of 29% more lamb output than S23 during the critical spring period (up to early June) would be of considerable practical significance in upland sheep systems, as would be the overall superiority of the tetraploid Meltra over S23.