Defined as the energy content of a feed (Gross Energy GE) minus the energy lost in faeces (Faecal Energy FE). The DE provides us with a useful estimate of the amount of energy available for use by the animal for any particular feed.
In Australia this is normally expressed as Megajoules per kg or MJ/kg. In the USA as Megacalories per kg or MCal/kg. One Megacalorie = 4.184 Megajoules.
The DE is an estimate of energy content derived form a standard formula using different weighting of various components such as carbohydrate fractions (ADF & NSC), protein, ash, and fat. To actually assess the precise DE of any feed would require a digestibility trial which is impractical for reasons of cost and being time consuming. The DE has inaccuracies caused by factors like ignoring the inclusion of gut lining cells in the faeces, variable digestibility of high fiber feeds like hay and the differing digestive efficiency between horses. Alternative systems such as the Net Energy NE system have been developed but are not yet in widespread use for horse feeds.