Botanical and nutritive content of the summer diet of sheep on a tall forb range in southwestern Montana.

Abstract

Sheep with esophageal fistulas were used to determine the botanical composition and the nutritive content of the diet at three periods during the summer grazing season on a high-elevation tall forb range. Grass made up almost one-third of the diet for the entire summer in 1966 and in early summer in 1967 but declined to only about 12% of the diet by late summer 1967. Sticky geranium comprised 35 to 49% of the available vegetation, but is quite unpalatable and contributed little to the diet. Northwest cinquefoil, the second most abundant forb, contributed more to the diet than any other forb. Mountain sorrel and pale agoseris, were consistently highly preferred but were relatively low in availability in the pastures and consequently did not constitute major portions of the diet. The amounts of preferred species in the diet were much higher on the first day than at the end of each trial because the supply of these species was depleted during the trial. The daily changes in diet as a result of utilization were greater for many species than the seasonal changes. Approximately three-fourths of the sheep's diet consisted of leaves in all three periods, The proportion of flowers in the diet increased significantly from early to late summer. In early summer, almost one-half of the sticky geranium eaten consisted of flowers. Daily changes in plant parts consumed were greater than the seasonal changes; leaves decreased while stems and flowers increased in the diet from the first to the last day of each trial. The crude protein content of the diet decreased significantly and the fiber and lignin content increased significantly from early to late summer. Green matter intake decreased somewhat and dry matter intake increased slightly from early to late summer.