Effect of glucose on fermentation heat in sheep rumen fluid in vitro.

1. Heat production rate (H) of rumen fluid was measured in a direct calorimeter. Basal H of samples of 15 ml rumen fluid mixed with 45 ml buffer was 0.4 mW/ml rumen fluid. 2. Addition of glucose (0.4-6.4 mg/sample) was followed by a dose-dependent increase in H. Maximal H was 1.1 mW/ml and lasted up to 5 min, returning thereafter to the basal level. 3. Expression of fermentation heat (Hf; kJ/mol substrate added) against glucose dose indicated an asymptotic dose response. 4. Maximal Hf (at infinite dilution) agreed with stoichiometric calculations whereas minimal Hf suggested a partial fermentation of the substrate at a high-glucose dose in the rumen environment.