Feed analysis

The feeds available to dairy herds fall into four main categories:

  • Forages
  • Concentrates
  • Moist feeds
  • Mineral and other supplements

They are generally assessed for their value in ruminant feeding on the basis of a number of specific  laboratory analysed parameters.

The most widely used of these are:

  • Dry Matter - DM (g/kg or %) The proportion of the feed that is not water - the higher the dry matter the less dilute the nutrient source.
  • Ash (g/kg DM or %) The amount of material in the DM that is not organic matter and so only of value to the animal for its mineral content.
  • Digestibility - D-Value (%) The extent to which the organic material contained in the dry matter is digestible.
  • Metabolisable Energy - ME (MJ/kg DM) The energy actually available to the cow after  accounting for losses in digestion, gases and urine.
  • Fermentable Metabolisable Energy - FME (MJ/kg DM) The amount of ME potentially available to the rumen microbes.
  • Neutral Detergent Fibre - NDF (g/kg DM or %) The total fibre content, also indicating the bulkiness of the feed.
  • Crude Protein - CP (g/kg DM or %) The total nitrogen content, including non-protein nitrogen as well as true protein.
  • Rumen Degradable Protein - RDP (g/kg DM or %) The amount of nitrogen available to the rumen microbes.
  • Digestible Undegradable Protein - DUP (g/kg DM or %) The amount of nitrogen available for digestion which escapes rumen degradation.

Some laboratories report measures as g/kg while others use percentages in their analyses. To convert g/kg into % divide by 10. To convert % into g/kg multiply by 10.

A range of other measures - including Acid Detergent Fibre (ADF), sugar & starch contents, lactic & butyric acid contents, ammonia nitrogen, Quickly Degraded Protein (QDP) and Slowly Degraded Protein (SDP) are variously also used to characterise feeds.