To obtain more information about rumen fluid composition, levels of different components are determined by a range of techniques which are often slow and cumbersome. This study was established to develop calibration equations for the rapid determination of the composition of rumen fluid with a view to monitoring changes in composition with time.

Forty-three strained rumen fluid samples, taken throughout a 7 h period from three lactating cows offered silage either alone or with fish meal or rapeseed meal/urea twice daily, were used. Immediately upon withdrawal from the rumen each sample was analysed for pH, then acidified using concentrated sulphuric acid before storing at -18°C. Following centrifugation at 11600 G concentrations of volatile fatty acids and ammonia-nitrogen were determined in the supernatant by packed column gas chromatography and enzymatically using glutamic dehydrogenase respectively.