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 hectare 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 averge 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 higher forage quality as measured by an array of parameters.
Ruff forage had a higher, less desirable grass tetany ratio
[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