Prediction of the true metabolizable energy concentration in forages for ruminants

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Abstract
A model has been developed to predict the true metabolizable energy (ME,) concentration in forages given to ruminants.The chemical description of forages is based on the concentrations of ash, crude protein, ether extract, sugars and α-glycans, β-glycans and lignin, volatile fatty acids and lactic acid. The model assumes complete fermentation of sugars, α-glycans and lactic acid. The extent of fermentation of β-glycans and crude protein is determined in part by rumen solid-phase outflow rate, which can itself be predicted from dry-matter intake.The model was tested using 121 graminaceous forages whose chemical composition and concentration of metabolizable energy had been measured in the Feedingstuffs Evaluation Unit at the Rowett Research Institute. The agreement between observed and predicted ME, for all classes of forage was nearly always as good as, or better than, the best prediction from single attributes of food chemistry which could only be determined retrospectively and were not consistent even within classes of forage. The model predicts a decline in ME, with increasing rumen solid-phase outflow rate which is determined mainly by the extent of fermentation of β-glycans.