Substitution Value of Birdsfoot Trefoil for Alfalfa‐Grass in Pasture Systems1

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Abstract
Conventional alfalfa (Medicago sativa L.)‐gass grazing systems do not permit sufficiently high animal intake of energy for high roducing ruminant animals. Provision of pasture swards containing a higher proportion of legume should increase energy intake. Our primary objective was to determine whether lamb daily gains could be increased by increasing the legume percentage in grazing systems via substitution of pure birdsfoot trefoil (Lotus corniculatus L) for alfalfagass as one‐third of the total rotational pasture. We compared four grazing systems for lambs in each of 3 years. The control system had an alfalfa‐smooth bromegrass (Bromus inermis Leyss.)‐orchardgrass (Dactylis glomerata L.) mixture in each of three rotationally grazed paddocks. A second system had orchardgrass in paddock 1, reed canarygrass (Phalaris arundinacea L.) in paddock 2, and smooth bromegrass in paddock 3; each grass was mixed with alfalfa. In the third and fourth systems paddocks 1 and 2 were identical to those in the control; paddock 3 in these systems had pure birdsfoot trefoil either grazed in sequence in late May or stockpiled for initial grazing in late June.Substitution of birdsfoot trefoil for alfalfa‐grass as one‐third of total seasonal pasture resulted in 22 to 24% increases in lamb average daily gains over a 3‐year period. The birdsfoot trefoil‐containing systems provided forage that had significantly higher legume composition, in vitro digestibility, crude protein concentration, and ap parent intake potential (lower concentration of cell walls) than did forage provided by the control (all alfalfa‐grass) system. The sometimes lower carrying capacity of the birdsfoot trefoil containing systems partly offset the greater gains of lambs on these systems. However, they provided a mean 17 to 18% increase in lamb product perha, com ared with all alfalfa‐grass systems. The birdsfoot trefoil containing systems also had lower overhead costs, because fewer animal units were required per unit of gain.The stage of maturation of birdsfoot trefoil at first grazing each year (immature vs. stockpiled) did not significantly influence animal performance or birdsfoot trefoil persistence. Use of a mixture of alfalfa‐smooth bromegrass‐orchardgrass in all paddocks (control), compared to orchardgrass, reed canarygrass, or smooth bromegrass as single species mixed with alfalfa in individual pad. docks, did not influence animal performance.A “pasture‐type,” creeping rooted alfalfa cultivar (‘Rambler’) did not persist as well as two “hay‐type” cultivars (‘Saranac’ and ‘Agate’). Invasion of weeds in the 3rd year proved to be a disadvantage of using pure stands of birdsfoot trefoil in grazing systems.