A Method for Determining Total Digestible Nutrients in Grazed Forage

Summary A method is presented for the determination of the TDN content of grazed forage. The digestibility of the organic matter is determined by the chromogen ratio technique by use of the formula: D = 100 − 100 A Y B X where D is the digestion coefficient for organic matter, A and B are the organic matter per gram of dry matter in the feces and forage, respectively, and X and Y are the chromogen per gram of dry matter in the feces and forage, respectively. TDN is determined by multiplying the digestion coefficient for organic matter, D, by a conversion factor calculated by the formula: F = M ( 100 + 0.000125 E ) where M is the per cent organic matter in the dry matter of the feed and E is the ether extract as per cent of the organic matter. Data are presented in support of the validity of the method. Evidence is shown which indicates that selective grazing may be more pronounced with mature than with immature forage.