Nutrients in ruminant feeding
The most important single measurement of the energy value is its digestibility. This can be determined either through an in vivo method, or in vitro by incubation with rumen fluid (Tilley and Terry, 1963) or pepsin and cellulose. More recently NIR spectroscopy has also been used to predict different digestibility fractions (in vivo energy calibrations for poultry, swine and ruminants are exclusively available via AusScan Online in partnership with Aunir).
Dry matter digestibility (DMD)
Determination of DMD is somewhat easier than organic matter digestibility as there are no additional ashing measurements involved.
DMD = (Feed dry matter - Faeces dry matter)/Feed dry matter
Organic matter digestibility (OMD)
If we correct the DMD value for ash we will get the OMD. This determination is preferred in certain circumstances, particularly when it can be used for the prediction of microbial protein synthesis.
OMD = (Feed organic matter - faeces organic matter) / Feed organic matter
Digestible Organic matter in dry matter (DOMD) or D value
The digestible organic matter content of dry matter is the most useful index particularly if the sample is contaminated with ash.
DOMD % = 100 x (Feed organic matter - faeces organic matter) / Feed dry matter
Metabolisable Energy (ME)
ME can be calculated from the DOMD
ME (MJ/kg) = DOMD x 0.16