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Rumen Removal Rates of some Chemically Defined Fractions of ¹⁴C-Labeled Alfalfa¹

Kansas State University, Manhattan

Abstract

Rumen removal rates of several plant fractions were determined, using ¹⁴C-labeled alfalfa at prebud, bloom and seed stages of maturity in separate trials with a mature, fistulated cow. A comprehensive scheme of analysis was used to determine lipid, soluble sugar, pectin, pepsin digestible protein, chlorite extractable lignin, hemicellulose, cellulose and acid insoluble lignin fractions of alfalfa and rumen dry matter. All constituents of the ¹⁴C-labeled alfalfa were removed from the rumen at a logarithmic rate. Stage of maturity did not affect removal rate of soluble sugar or lipid fractions. Removal rate of other fractions studied were slower after alfalfa reached the bloom stage. Further maturity appeared to have little effect on removal rates.

The soluble sugar fraction was removed most rapidly. The pectin, protein and lipid fractions generally were removed faster than were cellulose, hemicellulose and lignin fractions. However, cellulose was readily degraded rather than being left unmetabolized until the more available carbohydrates had been removed. Rumen microorganisms appeared to attack all nutrients simultaneously, but at different rates.

¹ Contribution No.717, Department of Dairy and Poultry Sciences, Kansas Agricultural Experiment Station, Manhattan. Data are in part from a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree in Animal Nutrition.

² Present address: Nutrena Mills, Cargill Building, Minneaapolis, Minn.

³ The assistance of E. L. Sorensen (Department of Agronomy, Kansas State University, and Crops Research Division, A.R.S., U.S.D.A.) in producing the ¹⁴C-labeled alfalfa is gratefully acknowledged.