Introduction The recent change in beef cattle support payments from headage to area based payment and relatively low cereal prices could see an increased interest in earlier finishing of beef cattle. An increased number of producers are therefore likely to adopt intensive cereal finishing systems for beef cattle. Antibiotic based feed additives e.g. monensin sodium, have been successfully used for over 40 years to manipulate microbial activity and improve beef cattle performance especially in cereal beef systems. The use of monensin sodium was banned from January 2006 and therefore there is a requirement to find alternative ‘natural’ products that can improve the efficiency of beef production with cereal based rations. Acid Buf is a natural rumen buffer derived from calcified seaweed (Lithothamnium calcareum) ground to a very fine particle size. It contains calcium and magnesium as well as a range of trace minerals. The claimed characteristics of Acid Buf are: excellent acid absorbency, long term buffering activity and fine particle size for optimum availability to help overcome problems with acidosis in high starch based rations. The objective of this experiment was to determine the effect of feeding Acid Buf on the performance of intensively finished dairy-bred beef cattle fed ad libitum cereals.