Estimation of Forage Nutritive Value from In Vitro Cellulose Digestion

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Abstract
Studies were conducted on the use of in vitro cellulose digestion (IVCD) as an estimate of in vivo forage nutritive value in terms of forage intake and energy availability. IVCD rate studies indicated that lag-time differences between forages were evident at 6, 12, and 18 hr, whereas incubation beyond 24 hr was essentially a measure of total digestion. An 18-hr value was used as an index of IVCD rate and a 30-hr value as a measure of total digestion. Within-trial variation associated with fermentation times (18 and 30 hr) and days was not significantly different. A lower variance was noted with one (bromegrass) out of 4 forages. Among-trial variances were greater than within trial. Adjustment for day-to-day variability, through the use of a control forage included in each trial, decreased among trial variability. Trials by substrate interactions were small, indicating no significant shift in fermentation curves of various substrates between trials. Correlation analysis indicated that intake (VIRI), DE, and NVI could best be estimated from 18-, 30-, and 18 x 30- hr IVCD values, respectively. The use of 18-hr IVCD in estimating NVI might be suggested due to lower standard errors of estimate. DE could be predicted accurately from IVCD, whereas indices including intake (RI, NVI) were more variable.