Abstract
The intake and digestibility of forages is largely influenced by the fibre content and specifically the neutral detergent fibre (NDF). Currently, the focus in commercial diet formulation and the modelling of animal performance is on the total NDF so as to achieve higher ruminant feed intakes, higher production performance and rumen health. Rations are often formulated for a specific level of NDF in the diet assuming that the digestibility of NDF operates over a narrow range. Forage NDF, particularly in C4 forages, varies greatly in potential digestibility within the rumen. This potential digestibility is defined as the NDF fraction which disappears after a long incubation period and the remaining indigestible component of NDF (iNDF) is unavailable for microbial digestion. It is hypothesized that this dietary iNDF has an important role in contributing to rumen digesta load and voluntary intake. Formulating a diet to a specific level of NDF without reference to the iNDF could markedly affect the resulting intake, digestibility and metabolisable energy (ME) content of the diet. It is concluded that nutritional models need to be modified to accept directly determined iNDF.
Highlights
The digestibility of forage and the capacity of ruminants to consume it, are largely influenced by its content of neutral detergent fibre (NDF)
Potential digestibility is defined as the NDF fraction which disappears after a long incubation period, leaving the indigestible component of NDF which is unavailable for microbial digestion [3,4]
The quantity of indigestible component of NDF (iNDF) in a forage-based diet plays a significant role in the regulation of the digestibility of diet and the feed intake of ruminants to which it is offered
Summary
The digestibility of forage and the capacity of ruminants to consume it, are largely influenced by its content of neutral detergent fibre (NDF). Diets are often formulated to a specific level of NDF with an underlying assumption being that the digestibility of that NDF spans a narrow range. When feeding temperate forages or corn silage this assumption holds true, when considering a broader selection of tropical (C4) forages the NDF does vary in ruminal digestibility, to an important extent. This digestibility of the fibre is directly related to potentially digestible portion of NDF (pdNDF) [1,2]. Formulating a diet to a specific level of NDF without reference to iNDF could markedly affect energy supply through reduced feed intake, digestibility and metabolisable energy (ME) content of the diet. Better assessment and awareness amongst nutritionists of the importance of iNDF for the range of tropical pasture species commonly used will improve the capacity of nutritionists to predict NDF digestibility and to more effectively develop balanced diets
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