Forage Quality, Mineral Constituents, and Performance of Beef Yearlings Grazing Two Crested Wheatgrasses

In the central Great Plains, crested wheatgrasses [Agropyron cristatum (L.) Gaetner and A. desertorium (Fischer ex Link) Schultes] are best utilized for early spring and late fall grazing. The principal objective of this study was to determine if beef (Bos Taurus L.) yearlings grazing ‘Ruff’ (A. cristatum) during the spring grazing season had higher average daily gains and gains per hectare than cattle grazing ‘Nordan’ (A. desertorum). These cultivars were evaluated in grazing trials (four replications) in eastern Nebraska in 1985, 1986, and 1987. The 0.8-ha pastures were seeded in the fall of 1983 on a Typic Argiudoll soil and were fertilized annually with 68 to 90 Kg N ha-1. Grazing was for 6 wk each spring by yearling steers with a beginning average weight of 250 kg. Averaged over 3 yr, Ruff produced higher gains per hectar than Nordan (272 vs 245 kg ha-1) probably because it produced more herbage because of its better persistence. At the end of the trial, the average basal cover of Ruff and Nordan were 21 and 6%, respectively. Three-year mean average daily gains were Ruff = 1.28 vs. Nordan = 1.34 kg d-1, which were unexpected, because Ruff generally had a higher forage quality as measured by an array of parameters. Ruff forage had a higher, less desirable grass tetany ration [K/ (Mg + Ca)] than Nordan (2.6 vs. 2.3) averaged over 3 yr. Cattle grazing Ruff had lower blood serum Mg levels than cattle grazing Nordan (15.4 vs. 16.2 mg L-1, both of which were below the hypomagnesemia threshold of 18 mg L-1. This condition may have reduced intake and animal gains. These results indicate the need for evaluating pasture and range grass cultivars under grazing conditions