Intra-caecal fermentation parameters in caecally-fistulated ponies offered barley based diets in which the barley had been physically processed by either rolling (RB), micronising (MB) or extruding (EB). Three ponies were offered 4 kg dry matter (DM) per day of either 100% hay cubes (HC), or one of three diets consisting of a 50:50 barley:HC mix. Due to small refusals of HC, the actual DM intakes (kg per day) were 3.74, 3.67, 3.57 and 3.52 (S.E.D. 0.18) for the HC, RB:HC, MB:HC and EB:HC diets, respectively. With the exception of butyrate, all intra-caecal fermentation parameters 4-8 h post feeding in ponies given diet RB:HC were significantly (P