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Collaborative in vitro Rumen Fermentation Studies on Forage Substrates¹

U. S. Department of Agriculture and Purdue University, Lafayette, Indiana²

Abstract

The magnitude of in vitrodigestion and the variability associated with the in vitrorumen fermentation technique was investigated in a collaborative study involving 17 laboratories. The in vitrodigestibility of cellulose and dry matter was obtained for three forage substrates, analyzed in three runs with duplicate determinations with length of incubation set at 6-, 12-, 24- and 48-hours.

Considerable variability occurred in the techniques employed by the different laboratories. The mean in vitrodigestibility for individual laboratories, after a 24-hr, fermentation period, ranged from 40.0% to 63.9% for cellulose and from 38.7% to 53.3% for dry matter. The interactions of laboratories with the length of fermentation time and with substrates were significant. Digestibility increased as the length of incubation increased, but at different rates for grass and legume substrates.

The development of a standard in vitroprocedure appears to be necessary if a more direct comparison of in vitroresults among laboratories is desired. The variability among laboratories was greater than among runs within laboratories, which was greater than between duplicate determinations within runs. The precision of the in vitromethods, as reflected in the variance estimates associated with runs and determinations within runs, did not differ greatly among laboratories, except for individual cases. The precision of the technique was greatest at the longer fermentation periods.

¹ Invited Paper Presented at the Symposium on Forage Evaluation, 56th Annual Meeting of the American Society of Animal Science, Knoxville, Tennessee. Journal Paper No. 2561 of the Agricultural Experiment Station, Purdue University.

² Crops Research Division, A.R.S., U.S.D.A. and Department of Agronomy, Purdue University.

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