Stoichiometery of organic matter fermentation of fresh and frozen-thawed forages 'in vitro'

Advances in understanding of the stoichiometry of the rumen have enabled a new approach to diet formulation. During incubation of feedstuffs with rumen fluid 'in vitro', volatile fatty acids (VFAs), CO2 and methane are produced as by-products of carbohydrate fermentation and their production is correlated with the rate of fermentation of organic matter (OM). The microbial crude protein (MCP) produced in the rumen is a function of the ATP generated within microbial cells by catabolism of feed OM and the efficiency of ATP utilization for polymer synthesis. Glucose content and ATP production can be calculated from VFA concentrations using the equations of Czerkawski (1986). The MCP can then be estimated by assuming that Y[ATP]=10.5 g cell DM per mol ATP (Payne, 1970). The aim of this study was to investigate differences in fermentation characteristics between fresh and frozen-thawed forages.