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 previously well-managed permanent grassland sward of indigenous (unsown) grass species and two ryegrass reseeds, managed within intensive silage-production systems, to support the production of beef. Replicate plots within an existing old permanent grassland (OPG) sward were left as OPG or reseeded with Lolium perenne (LP) or Lolium multiflorum (LM). During each of the 3 years after reseeding, the annual production of OPG and LP swards were each composed of four growths with similar harvest dates, while five growths of the LM sward were harvested annually. All swards had similar annual fertiliser 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 libitum) the four or five harvests of silage, in sequence, for 126 days, supplemented daily with 2.0 kg concentrates per head. In year 2, 99 finishing heifers were divided into nine groups and offered (ad libitum) the silages from 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 the OPG, LP and LM swards, with corresponding values for the yield of digestible DM of 29.6, 31.5 and 34.1 (s.e. 1.16; P < 0.05) t/ha. Grass ensilability 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 significantly affected by sward type. In year 2, heifers offered silage from the primary 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. Overall, carcass output per ha was higher for LP and LM swards than OPG. Ranking swards in terms of grass DM yield, even modified for differences in digestibility, can incorrectly indicate the attractions of reseeding.