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Relation of Certain End Products of Rumen Fermentation to Forage Feeding Value^{1, 2,}

Michigan State University, East Lansing

Abstract

Oat straw and alfalfa-bromegrass hay were compared by conventional TDN determinations and by in vitro volatile fatty acid production and cellulose disappearance. Alfalfa-bromegrass hay contained 2.4% more TDN than a ration of oat straw plus a protein, vitamin and mineral supplement. Four dry Holstein cows voluntarily consumed an average of 23 lb. of alfalfa-bromegrass hay while a similar group ate an average of 13.5 lb. of oat straw per head daily. During in vitro fermentation alfalfa-bromegrass hay produced volatile acids at a significantly (P<.05) faster rate than oat straw. The acetic to propionic acid ratio was significantly (P<.05) lower for alfalfa-bromegrass for the first 4 hours, but not significantly different for the balance of a 24-hour in vitro fermentation.

The cellulose of oat straw disappeared at a slower rate than that of alfalfa-bromegrass hay early in the in vitro fermentation; however, after 24 hours there was no significant difference in the amounts of cellulose which had disappeared from either oat straw or alfalfa-bromegrass hay. In vitro differences in ratio and amounts of volatile fatty acids produced were greatest when inocula were obtained from steers fed the same forage as that being used for in vitro substrate.

¹ Published with the approval of the Director of the Michigan Agricultural Experiment Station as Journal Article No. 2871.

² The data contained in this paper are a portion of the research thesis presented by the senior author in partial fulfillment of the requirements for the degree of Doctor of Philosophy, School of Advanced Studies.

³ Department of Animal Husbandry, Michigan State University, East Lansing.

⁴ Present address: Dept. of Animal Science, University of Wyoming, Laramie.

⁵ Department of Biochemistry, Michigan State University, East Lansing.