Prediction of the rumen fermentable organic matter content by an enzymatic method

Abstract

In the Dutch protein evaluation system (Tammingaet al., 1994) microbial protein synthesized in the rumen is estimated from the fermentable organic-matter (FOM) content. The reference method to determine FOM is byin situincubations of food in the rumen of fistulated animals. However, this is a cumbersome, time-consuming and expensive procedure. In practice, FOM is estimated from the digestible organic-matter content (DOMD) corrected for crude fat (Cfat), rumen escape protein (EP) and starch (ES) and the fermentation products (FP), using tabular values. Apart from being indirect, this approach takes little or no account of the variability within foods. Although anin vitromethod based on rumen fluid may give a good prediction ofin situFOM for the majority of the foodstuffs (Coneet al., 1994), an enzymatic method is preferable for practical reasons. From the organic-matter (OM) degradation by a mixture of amylase and other carbohydrate degrading enzymes at 39°C during 0, 2, 6 and 24 h, Coneet al. (1996) obtained a moderate correlation within situFOM for 29 grass and grass silage samples (R2= 0.88; residual s.d. = 37 g/kg dry matter (DM)) and 80 samples of concentrates, maize and clover (R2= 0.77; residual s.d. = 42 g/kg DM). In this study a modified version of the enzymatic method of de Boeveret al. (1994), normally used to predict thein vivoOM digestibility and energy value of concentrates, was tested for its reliability to predictin situFOM of compound foods and forages.