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In the semi-arid region of southwestern Saskatchewan, the long-term persistence of alfalfa (Medicago sativa L.) in seeded pasture mixtures with commonly used grass species, such as crested wheatgrass (Agropyron cristatum L. Gaertner) or Russian wildrye (Psathyrostachys juncea Fish. Nevski), is maximized by seeding it in separate alternate rows or in rows running perpendicular to the grass. These patterns, however, can result in preferential grazing of the alfalfa and increased risk of ruminant bloat. The inclusion of slender wheatgrass [Elymus trachycaulus (Link) Gould ex Shinners], a short-lived but rapidly establishing perennial grass, in the same space with alfalfa had been ProPosed to reduce alfalfa forage yield and ruminant bloat hazard and increase early stand production in mixtures with slowly establishing grasses. Alfalfa forage production was reduced when slender wheatgrass dominated the mixture (> 50%). The slender wheatgrass plants disappeared within 3 to 5 yr after seeding, and subsequent alfalfa yield from slender wheatgrass mixtures was the same as the alfalfa-alone treatment. Slender wheatgrass was eliminated more rapidly when the grass associate was crested wheatgrass than when it was Russian wildrye. In the third year after seeding, there was a 40% loss of slender wheatgrass in Russian wildrye stands. The inclusion of slender wheatgrass did not improve total forage production in the first 2 yr after seeding for the slowly establishing Russian wildrye.