The potential digestibility of cellulose in forage and faeces

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Abstract
The potential digestibility of cellulose is defined as the maximum digestibility obtainable when the conditions and duration of digestion are not limiting factors. Techniques for measuring potential cellulose digestibility were examined and the relationship between potential cellulose digestibility and in vivo cellulose digestibility was explored for a range of grasses.Cellulose digestibility was found to reach a maximum value after 5 days incubation in vitro. No further cellulose was digested when the residues from an initial incubation for 6 days were incubated with a second rumen liquor inoculum. The values measured after a single incubation of 6 days duration were similar to cellulose digestibility coefficients measured by the suspension of ground forage samples in nylon bags in the rumen for 6 days. Plant factors appear to limit further digestion and the residue from prolonged digestion in vitro consisted only of lignified and cutinized tissue. Potential cellulose digestibility measured by either of the above techniques was higher than cellulose digestibility in vivo. The difference varied between forages and when the difference was large, the digestibility of cellulose in faeces was high.It is suggested that measurements of the potential digestibility of cellulose in feed and faeces may be of use in estimating the digestibility of grazed herbage.