Physically processed cereals and legumes make up a large proportion of the concentrate proportion of diets for equines. The effects of processing on digestibility of cereals has been investigated relatively few studies have investigated the effects on intra-caecal fermentation parameters and degradation rates. The objective of this thesis was to investigate the effects of processing on intra-caecal fermentation parameters and to develop in sacco methodologies which would allow determination of degradation rates. In the first set of experiments three caecally fistulated ponies were 4 kg DM per day of either 100% hay cubes (HC) or one of three diets consisting of 50:50 barley:HC mix. The barley in the mixed diets was either rolled (RB), micronised (MB) or extruded (EB). Inclusion of RB in the diet significantly (P<0.05) reduced intra-caecal pH and acetate molar proportions whilst lactate concentration and propionate molar proportions were increased (P<0.05) compared with the HC diet measured 5 hours post feeding. Different physical processing methods did not alter total tract in vivo apparent digestibilities nor the digestible energy or digestible crude protein contents of the barley diets which averaged 14.8 MJ/kg DM and 86 g/kg DM respectively. Mean retention times (MRT) of digesta was also determined for the four diets and were 46.1, 42.3, 46.9 and 43.0 h for HC, RB, MB and EB respectively. There were no differences between diets in terms of MRT. In the second set of experiments barley, maize and peas that had undergone either micronisation or extrusion were incubated in situ in the caecum of ponies to determine degradation parameters and to investigate the effect of incubation sequence on degradation parameters. Compared to unprocessed feeds, micronisation significantly increased (P<0.05) effective degradabilities (ED) of starch for barley and maize but reduced the ED of crude protein. Extrusion increased the ED of CP for maize. ED of peas were not affected by either processing method. Incubation sequence had no significant effect on degradation parameters of starch-based feeds.