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Studies on the In Vitro Rumen Procedure: Improved Inoculum Preparation and the Effects of Volatile Fatty Acids on Cellulose Digestion^{1, 2,}

Ohio Agricultural Experiment Station, Wooster⁴

Abstract

An improved inoculum for in vitro rumen fermentations has been prepared by discarding the first extraction of the rumen contents, resuspending the pressed pulp in buffer, and re-expressing this liquor as an inoculum source. Inoculum prepared from this liquor gave higher cellulose digestion and less variation between experiments. The activity of these cells was destroyed completely by washing twice with buffer. Aeration for 15 minutes destroyed only 40% of the activity of this inoculum while incubation at 37° C. for 2 hours destroyed only 23% of the activity.

A mixture of acetic, propionic and butyric acids (300, 300, and 30 mg./per 100 ml., respectively) inhibited cellulose digestion. Butyric acid alone, however, at levels of 100 to 150 mg./1OO ml. of medium possessed cellulolytic-factor activity similar to that demonstrated by 10 to 30 mg. of valeric acid. The significance of these findings is discussed.

¹ Approved for publication as Journal Article No. 29–58 by the Associate Director of the Ohio Agricultural Experiment Station. A preliminary report of this investigation was presented before the 49th meeting of the American Society of Animal Production, November, 1957, and the Abstract appears in the J. Animal Sci. 16:1088 (1957)

² The studies reported herein were supported in part by a Grant-in-Aid from Swift and Company, Chicago, Illinois.

³ Present address: Department of Animal Industries, Connecticut Agricultural Experiment Station, Storrs, Connecticut.

⁴ Department of Animal Science.