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

This study was designed to evaluate the effect of the physical form of a ha y diet on (1) in situ DM and NDF degradation rate and (2) postprandial evol ution of pH and VFA concentrations, in the cecum and the right ventral colo n of ponies. Four gelded ponies, fitted with cannulae in the cecum and the right ventral colon, were kept on wood shavings and fed twice daily a maint enance 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 offer ed 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 incubati on 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 po st-feeding. Grinding and pelleting the hay caused a significant decrease in both the ra te and the extent of in situ fibre degradation. However, they did not alter significantly the apparent digestibility of fibre (Drogoul et al., 2000), in spite of a significant 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, fibre digestion in the hindgut of ponies is a function of both t he time available for digestion and the microbial degradation rate. The rat es of disappearance of DM and fibre from bags in the cecum and the right ve ntral colon were similar. Because the MRTs of both particles and solutes we re much higher in the colon than in the cecum (Drogoul et al., 2000), our r esults showed the more significant role of the colon relative to the cecum in fibre digestion in the ponies. (C) 2000 Elsevier Science B.V. All rights reserved.