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The Composition and Apparent Digestibility of Bluestem Grass in the Growing Stage, and in the Dry and Hay Stages when Supplemented with Cottonseed Cake

Oklahoma Agricultural Experiment Station

Abstract

The composition of native pasture grass, predominantly bluestem, being grazed by steers was determined at frequent intervals during the grazing season and winter of 1942–43. From late in May until the middle of September the dry matter of the grass varied from 32.7 percent to 39.0 percent. The composition of the dry matter during those months varied from 6.77 percent to 8.97 percent in protein and from 28.46 percent to 32.32 percent in crude fiber. After September protein decreased to 4.31 percent and crude fiber increased to about 34 percent. Further decrease of protein to 2.56 percent without a corresponding increase in crude fiber took place during the winter. Variations in N-free extract were small and irregular throughout the summer and winter.

The digestibility of the grass was determined during periods when the steers were individually fed in dry lot and during periods when they were allowed to graze the pasture. Grass intake during the grazing periods was calculated from the dry-matter consumption: defecation ratios determined for each steer during dry lot periods which either preceded or immediately followed the grazing periods.

The apparent digestibility of dry matter, protein, and crude fiber of the grass was lower in June than in July, August and September. During the latter months there was practically no change in the digestibility of the nutrients, with the exception of protein and ether extract. The apparent digestibility of dry matter, protein, crude fiber, and N-free extract decreased from about 58 percent, 54 percent, 69 percent, and 61 percent, respectively, in September, to about 41 percent, –16 percent, 62, percent, and 41 percent, respectively, in November.

The digestibility of the dry winter grass was somewhat higher in December than in January and February. Supplements of cottonseed cake improved the digestibility of both winter grass and prairie hay rations. The dry matter of the late winter grass was less digestible than that of cured hay.

Digestion trials conducted during gracing periods gave some evidence that the fecal excretion of nitrogen and ether-soluble material is greater in steers on pasture than in steers in dry lot.

¹ Present address, Department of Animal Husbandry, South Dakota State College, Brookings.

² Present address, American Hereford Association, Kansas City, Missouri.