Physically effective fibre in ruminant nutrition: A review

Ruminants require fibre in coarse physical form described as the “physically effective fibre” which has a significant effect over chewing and ruminal activity. Physically effective NDF (peNDF) is defined specifically as the fraction of fibre that stimulates chewing activity and is primarily related to the particle size. Increasing fibre content and physically effective NDF enhances saliva flow, acetate to propionate ratio, milk fat levels and maintains the rumen pH. An appropriate level of NDF and the particle size in the ruminant diet will increase the dry matter intake and its digestibility and has a positive impact over the ruminant performance. According to National Research Council (NRC), NDF content should be maintained at 25 per cent of dietary dry matter with at least 75% from forage. PSPS is commonly and routinely used separator to express the particle size distribution, and to calculate the content of peNDF. Till now no recommendations are given for the physically effective fibre due to lack of standards and validated technique to quantify the physically effective properties of fibre in the diet.