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The Apparent Digestibility of Prairie Hay of Variable Protein Content, with Some Observations of Fecal Nitrogen Excretion by Steers in Relation to Their Dry Matter Intake

Oklahoma Agricultural Experiment Station

Abstract

In an investigation of the apparent relationship between the proximate composition of prairie hay and its nutritive value, digestion trials were carried out with steers receiving prairie hay, alone, and supplemented with varying amounts of cottonseed meal. Total digestible nutrients of the hay increased in a fairly uniform manner from 41 percent to 56 percent as the protein content of the hay increased from about 3 percent to 6 percent.Likewise, crude fiber digestibility increased from 56 percent to 69 percent while the apparent digestibility of protein increased from negative values to 41 percent.

When cottonseed meal in amounts varying from 0.5 lb. to 3 lbs. daily was fed as a supplement to 10 lbs. of hay, differences in digestibility related to the protein content of the hay were again apparent. The digestibility of dry matter in the high-protein hay was equal to that in rations made up of average or low-protein hay supplemented with 2 lbs. of cottonseed meal

A close relationship between protein content and digestibility of nutrients in hay is indicated in these results.

Wastage of protein in digestion, expressed as nitrogen lost in the feces per 100 grams of dry matter intake, varied only slightly from 0.55 gram when hay alone was fed and increased to about 0.71 gram when cottonseed meal was fed as a supplement. It is suggested that when conditions permit the feed consumption of grazing animals can be determined by taking ad-vantage of the relationship between fecal nitrogen excretion and dry matter intake.

¹ Departments of Agricultural Chemistry Research and Animal Husbandry, respectively, Stillwater, Oklahoma.