This month we take a look at fibre. It is a standard parameter in NIR analysis but what do the figures really tell us?
NDF (Neutral Detergent Fibre) is determined by boiling samples with a neutral detergent which breaks down the cell wall, allowing the cell contents (the highly digestible portion) to be removed. The remaining residue after drying is called NDF. NDF predominantly consists of cell wall material (cellulose, hemicellulose and lignin) plus Ash. NDF is used to calculate dry matter intake by the animal.
ADF (Acid Detergent Fibre) on the other hand is determined by treating the sample by an acidified detergent which solubilises the Hemicellulose portion in the sample. ADF is used to calculate digestibility.
Crude Fibre is determined by an older method that involves boiling the sample with sulphuric acid and sodium hydroxide under controlled conditions. The loss of weight resulting from ashing the dried residue corresponds to the Crude Fibre. This does not fully reflect the lignin content, does not include ash and normally is not a good indication of digestibility.
The following relationships can be concluded from the above:
ADF = NDF - Hemicellulose
Crude fibre < ADF < NDF