Evaluation of Forages in the Laboratory. IV. Within and among Trial Variability of the Wisconsin Artificial Rumen Procedure

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Abstract
Within and among trial variability of an artificial rumen procedure used for forage evaluation were estimated. Comparison of forages ground through a 40-or 60-mesh screen revealed that finer grinding increased in vitro digestibility of grasses and legumes but the digestibility of grasses was increased to a greater extent. No significant difference was found in the correlation of in vitro cellulose digestion and in vivo DDM due to fineness of grind. It was suggested that grinding be standardized within a laboratory. Fermentation periods of 18, 24, 30, and 48 hr all resulted in cellulose digestibilities significantly correlated with in vivo DDM. The correlation coefficients did not differ significantly. Day-to-day variation was significantly less for the 48-hr fermentation than for any of the shorter times. Alternate procedures involving either a flask or a beaker as the fermentation vessel did not yield different within or among trial variances. The beaker method has the advantage of eliminating transfers. The over-all variance and coefficient of variation of the Wisconsin artificial rumen procedure were 2.74 and 3.54% within day and 1.48 and 1.92% among days, respectively.