Pasture legumes that persist under challenging agro-ecological conditions are crucial to ensure high lamb growth rates in dryland pastures. Pasture and lamb production from white clover (TF-Whc), birdsfoot trefoil (TF-Bft), balansa clover (TF-Bc) and subterranean clover (TF-Sc) planted with tall fescue either as binary mixtures or as a diverse combination of all (TF-Mix) were compared in a summer-dry hill site in Corvallis, Oregon over a two-year period. In 2018, all pasture combinations provided similar lamb liveweight gains (LWG, mean 177 g d-1) in the first half of spring. Lambs in TF-Bc and TF-Mix pastures grew 31 to 41 g d-1 faster than those grazing TF-Sc, TF-Whc and TF-Bft in the second half of spring (P<0.05). Overall, TF-Bc and TF-Mix had higher (P<0.05) legume content (32 and 37% respectively) compared to other pasture combinations. In spring 2019, lambs that grazed TF-Mix and TF-Whc pastures had higher LWG than those on other pastures (P<0.05). The superior lamb growth rates were associated with the higher legume content and pasture quality maintained into the late spring period. Overall, the legume content of all pastures decreased over the course of the two-year trial with the decline being substantial for balansa clover. The present study confirmed that high legume content of pastures leads to greater lamb growth rates. Total annual DM yield of
the pastures that had greater legume content were superior to others (P<0.05). Combination of self-regenerating annual clovers with perennial legumes in pasture mixtures may ensure higher legume content and longer persistence in dryland hill pastures
