Feeding ground and pelleted hay rather than chopped hay to ponies 2. Consequences on ®bre degradation in the cecum and the colon

This study was designed to evaluate the effect of the physical form of a hay diet on (1) in situ DM and NDF degradation rate and (2) postprandial evolution of pH and VFA concentrations, in the cecum and the right ventral colon of ponies. Four gelded ponies, ®tted with cannulae in the cecum and the right ventral colon, were kept on wood shavings and fed twice daily a maintenance diet composed of equal parts of Lucerne and Cocksfoot hay. The hay, either chopped (CH) or ground (1.5 mm screen) and pelleted (GPH), was offered to the ponies at the same level of DM intake in a crossover design. The in situ disappearance of hay DM and NDF was measured during a 48 h incubation period in the cecum and the colon. Cecal and colonic VFA concentrations, and pH were measured before the morning feed, then every hour until 8 h post-feeding. Grinding and pelleting the hay caused a signi®cant decrease in both the rate and the extent of in situ ®bre degradation. However, they did not alter signi®cantly the apparent digestibility of ®bre (Drogoul et al., 2000), in spite of a signi®cant increase in mean retention time (MRT) of both the liquid and particulate phases of digesta. This phenomenon may result from a decrease of the cellulolytic activity. These results suggest that, as in ruminants, ®bre digestion in the hindgut of ponies is a function of both the time available for digestion and the microbial degradation rate. The rates of disappearance of DM and ®bre from bags in the cecum and the right ventral colon were similar. Because the MRTs of both particles and solutes were much higher in the colon than in the cecum (Drogoul et al., 2000), our results showed the more signi®cant role of the colon relative to the cecum in ®bre digestion in the ponies. # 2000 Elsevier Science B.V. All rights reserved.