In order to understand and ultimately predict the voluntary intake and performance of ruminants, it is necessary to know the nutritional value of foods. Most recent systems for predicting nutrient supply are dynamic in nature and characterize foods in terms of the quantities of available nutrients and their potential rates of supply. The in vitro gas production system has been used to characterize the carbohydrate fraction of foods in this manner. For the technique to be able to do this, two assumptions must be satisfied. First, that the rate of fermentation is limited by characteristics of the food and secondly that the pattern of gas production correlates closely with the pattern of food fermentation.Low microbial activity within the system could invalidate both assumptions since it could (i) limit the rate of food fermentation, thus not allowing the potential rate determined by the physical and chemical nature of the food to be measured and (ii) result in partition of food carbohydrate into new microbial matter, thus reducing the amount of volatile fatty acids and hence gas produced per unit of food fermented.
The aims of this study were mathematically to simulate food fermentation within an in vitro system and to use this representation to investigate the potential effects of variation in microbial activity on the characterization of foods.