The other conclusion that can be drawn for the data presented thus far is that ruminal fermentation of corn and grass silages is indeed enzyme-limited. Bhat et al.(1988) concluded that the rate of adhesion of cellulolytic microorganisms did not limit the rate of degradation of barley straw in the rumen. Dehority and Tirabasso(1998) manipulated the population size of cellulolytic bacteria in the rumen of sheep by changing the diet, but the rate of digestion of alfalfa cellulose was unaffected,indicating that “the concentration of cellulolytic bacteria is not the limiting factor in the digestion of cellulose in the rumen.” Other factors, such as the specificity of enzyme activity that might benefit ruminal fermentation most, have not been investigated. However, it is clear from the present experiments that increasing enzyme activity in ruminal fluid does increase the rate of fermentation, albeit at concentrations that cannot be provided by present feed supplements.
The next aim was to attempt to identify which, if any, of the enzyme activities that were present in the different preparations was rate-limiting in ruminal fermentation of the silages.