To determine if beef bulls adjust their chewing pattern to avoid ruminal acidosis, the chewing behaviour of double-muscled (dm) and non-dm bulls was studied with a concentrate based diet, with and without maize silage. Conformation (dm or not) did not infl uence the chewing behaviour. Daily rumination time was more strongly affected by the roughage portion than the daily eating time. Removing the maize silage induced a shift towards more rumination during the night. Conclusively, bulls did not adjust their chewing pattern to the acidotic rumen load.