The Role iNDF in the Regulation of Feed Intake and the Importance of Its Assessment in Subtropical Ruminant Systems (the Role of iNDF in the Regulation of Forage Intake)

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.