Rumen acidosis, acute and sub-acute, is an ongoing bane of the dairy and feed-lot sectors, resulting in animal deaths, morbidity and diminished productivity (Owens et al., 1998). Major impediments to improving understanding of these conditions include the large range of animal responses observed under identical conditions (Schwartzkopf-Genswein et al., 2003) and the difficulty encountered in measuring rumen pH itself, which has historically required either rumen cannulation or oesophageal intubation, both of which are likely to affect animal behaviour.