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Ruminal NH³, pH and VFA of Beef Cattle on Orchardgrass Pasture and Self-Fed Liquid Molasses-Urea or Ground Corn-Fat Supplements

U.S. Department of Agriculture, Beltsville, Maryland 20705

Abstract

Ruminal fermentation end-products were studied in 116 cattle which grazed orchardgrass pastures at three intensities and were offered, on an ad libitum basis, either no supplement, liquid molasses plus urea or ground corn plus fat. Total ruminal volatile fatty acids increased as grazing intensity decreased. Ruminal pH, NH₃ and individual volatile fatty acids were not affected by grazing intensity. The supplements were consumed in equal amounts on an as-fed basis; however, the corn supplement contained twice as much net energy compared to the molasses supplement. Both supplements tended to lower ruminal pH. Corn-fat supplements lowered ruminal ammonia while molasses-urea supplemented animals were intermediate but closer to the control animals. The patterns of individual volatile fatty acids for the corn-fat animals resembled those of animals on a high concentrate diet while the relative proportions of acetic and propionic acids in the molasses-urea animals resembled the controls. There was a trend toward increased butyric acid and decreased isobutyric and isovaleric acids when the molasses-urea supplement was fed. The results of this study indicated a greater shift from cellulolytic to amylolytic fermentation occurred in the rumen when the corn-fat supplement was fed compared to the molasses-urea supplement.

¹ Animal Science Research Division, A.R.S., Beltsville, Maryland 20705.

² Crops Research Division, A.R.S., Beltsville, Maryland 20705.

³ The authors gratefully acknowledge the assistance of Annie Rolle and Arlan Evans in the analysis of samples and Drs. L. L. Slyter and D. A. Dinius in the examination of rumen microorganisms and the determination of in vitro digestibilities.