Rate and Extent of In Situ Digestion of Medium and High Quality Alfalfa and Orchardgrass Neutral Detergent Fiber as Determined by Extended Periods of Incubation Time

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Abstract
Neutral detercent fiber fractions obtained from high and medium quality alfalfa and orchardgrass were incubated in situ for up to 240 h. Although initial samples contained 100% NDF, residues left after incubation were contaminated by non-NDF-material. Parameter estimates of the potentially digestible fraction, rate of digestion, and lag times for NDF of both high and medium quality alfalfa became stable well before 48 h. Estimates of potentially digestible fraction, rates of digestion, and lag times at 48 h were 50.38%, .107 h-1 and 3.69 h for high (in vitro DM digestibility = 86.6%) and 41.57%, .109 h-1, and 3.24 h for medium quality (in vitro DM digestibility = 78.2%) alfalfa. Stable parameter estimates did not occur until 72 h in the high quality orchardgrass (in vitro DM digestibility = 87.8%), and estimates for medium quality orchardgrass (in vitro DM digestibility = 64.6%) did not stablilize until 144 h of incubation. Parameter estimates of potentially digestible fraction, rate of digestion, and lag times at 72 h for high quality orchardgrass were 69.75%, .169 h-1, and 3.91 h and those for medium quality orchardgrass at 144 h were 56.03%, .042 h-1, and 10.69 h, respectively. Results indicate that use of less than 72 h in situ values as an estimate of indigestible fiber may overestimate indigestible fiber, even in medium quality forages.