Comparison of old permanent grassland, Lolium perenne and Lolium multiflorum swards grown for silage 1. Effects on beef production per hectare

The aim was to determine the relative potential of the annual output of a p reviously well-managed permanent grassland sward of indigenous (unsown) gra ss species and two ryegrass reseeds, managed within intensive silage-produc tion systems, to support the production of beef. Replicate plots within an existing old permanent grassland (OPG) sward were left as OPG or reseeded w ith Lolium perenne (LP) or Lolium multiflorum (LM). During each of the 3 ye ars after reseeding, the annual production of OPG and LP swards were each c omposed of four growths with similar harvest dates, while five growths of t he LM sward were harvested annually. All swards had similar annual fertilis er inputs. During years 1 and 2, all crops were ensiled separately. In year 1, 97 finishing steers were divided into three groups and offered (ad libi tum) the four or five harvests of silage, in sequence, for 126 days, supple mented daily with 2.0 kg concentrates per head. In year 2, 99 finishing hei fers were divided into nine groups and offered (ad libitum) the silages fro m the first growth, second growth or remaining growths combined of the OPG, LP and LM swards, for 103 days. The cumulative mean dry matter (DM) yields over the 3 years were 40.4, 41.4 and 44.8 (s.e. 1.55; P > 0.05) t/ha for t he OPG, LP and LM swards, with corresponding values for the yield of digest ible DM of 29.6, 31.5 and 34.1 (s.e. 1.16; P < 0.05) t/ha. Grass ensilabili ty indices suggested the most difficult average preservation challenge was for herbage from the OPG sward and least difficult for herbage from the LM sward. In year 1, neither silage DM intake nor carcass gain were significan tly affected by sward type. In year 2, heifers offered silage from the prim ary growth of OPG had a lower (P < 0.05) intake and carcass gain than those offered the primary growth of LP or LM. For silages from the second growth , LM supported higher intake and carcass gain (P < 0.05) than LP or OPG. Ov erall, carcass output per ha was higher for LP and LM swards than OPG. Rank ing swards in terms of grass DM yield, even modified for differences in dig estibility, can incorrectly indicate the attractions of reseeding.