Submitted to: The Skjervold Symposium
Publication Type: Proceedings
Publication Acceptance Date: September 24, 2003
Publication Date: October 23, 2003
Citation: Mertens, D.R. 2003. Effect of plant maturity and conservation methods on fibre charcteristics and nutritive value. Proceedings of The Skjervold Symposium. p. 17-34. Technical Abstract: Dietary fibre is a nutritional concept that describes those feed components that are most difficult to digest. To accurately measure it, a method must match a relevant nutritional definition of fibre. For ruminants and herbivorous animals, a logical definition of fibre is "those fractions of feed that are indigestible or slowly digesting and occupy space in the gastrointestinal tract." This definition describes the insoluble dietary fibre of feeds and, of the routine methods that are currently in use, only neutral detergent fibre (NDF) fits this definition. Of the various modifications of the NDF method, only the amylase-treated NDF (aNDF) method has been demonstrated to be reproducible among laboratories on a wide range of feeds. Because aNDF is an empirical method, it must be followed exactly to obtain accurate results. As plants mature aNDF increases, as does its lignin content, and its digestibility declines. Because the aNDF of legumes contain a greater proportion of lignin, it is less digestible than that in grasses. Ensiling grasses results in a decrease in aNDF concentration, when adjusted for soluble matter losses, due to enzymatic and acid hydrolysis of hemicelluloses. Because aNDF is the feed fraction with incomplete and variable digestibility, it is a key element of simple and complex summative equations used to estimate digestibility. Because aNDF is related to the filling effect and energy value of feeds, it is also related to intake regulation. The NDF-Energy Intake System uses NDF content of forages and concentrates and the energy demand of the animal to quantitatively predict the ration characteristics that maximize forage intake. When minimum forage rations are desirable, aNDF and particle size can be combined in a single value, physically effective NDF, that can be used to insure that the minimum effective fibre requirement of dairy cows is met.