Growth, Physiological Responses, and Evidence of Toxicity in Yearling Dairy Cattle Grazing Different Grasses

Three different sets of six or eight experimental grazing plots of approximately 1.2 ha each were used in 12 seasonal grazing trials with yearling dairy cattle by the put-and-take method during 12 years to evaluate the nutritive qualities of pure seedings of grasses. All grasses were fertilized and managed for good animal performance. Incidence and symptoms of fescue toxicity were noted. In the first three trials, the average daily gains, in order, for orchardgrass, smooth bromegrass, Kentucky 31 and G1-43 tall rescue were 0.57, 0.60, 0.37, and 0.11 kg. Dry matter intake on G1-43 rescue was reduced. Dry matter digestibilities were similar. In the 4th and 5th trials average daily gain on 45-50 tall fescue was reduced. In Trials 7 and 8 respiration rates and rectal temperatures were increased on 45-50 and Kenwell tall rescue. In Trials 9, 10, and 11 the values for Kentucky synthetic orchardgrass, Kentucky 31 tall rescue, and a perennial ryegrass-tall rescue hybrid derivative were average daily gain 0.65, 0.76, and 0.36 kg; respiration rate 36, 36, and 56 per minute; and rectal temperature 39.5, 39.4, and 39.8 C. There were generally statistically significant differences between the rescues and the other grasses, though Kentucky 31 and Kenwell varieties