Calorimetric determination of the degradation rate of rapidly fermentable organic matter of forages

Abstract

Degradation characteristics of organic matter of grass forages was determined by measuring the disappearance of organic matter from dacron bags incubated in the rumen of cows as well as from the fermentation heat of feeds incubated in vitro with rumen fluid. Data from dacron bags were used for evaluation of the pool size of rapidly and slowly degraded organic matter components in feeds. Fermentable organic matter, calculated from fermentation heat data, were used for the evaluation of the rate of degradation of rapidly degradable organic matter in feeds. Rapidly degradable organic matter comprised 36, 36 and 13% of corn silage, wheat silage and wheat straw, respectively. Slowly degradable organic matter pools were 29, 20 and 29% of these feeds. Rates of degradation of the slowly degradable organic matter were 5, 3 and 2% h −1. Degradation rates of the rapidly degradable component were 17, 19 and 9% h −1. Evaluation of organic matter pool size and degradation rates are required for assessment of energy availability and microbial synthesis. Hence, a combination of in vitro fermentation heat measurements of feeds, together with determination of organic matter disappearance from dacron bags in the rumen, may provide useful information for characterization of the rate of energy digestion of feeds in the rumen.