Feeding and microbial disorders in horses: 2: Effect of three hay : grain ratios on digesta passage rate and digestibility in ponies

Digesta passage rate and digestibility of diet components (dOM, dNDF and dA DF) were measured in the entire digestive tract of six ponies to determine the effects of the dietary hay:grain ratio on die efficiency of fiber diges tion. Three diets based on chopped meadow hay and rolled barley were tested in a 3x3 Latin square experiment: 100% hay (100:0, 114gDM/KgBW(0.75)/day), 70% hay-30% barley (70:30, 69gDM/KgBW(0.75)/day) and 50% hay-50% barley (5 0:50, 58gDM/KgBW(0.75)/day). Particles markers (Europium for hay and Ytterb ium for barley) and a solute mark-er (Cr-EDTA) were used for passage rate m easurements. As the proportion of barley in the diet increased, DM intake d ecreased and mean retention time (MRT) of all markers increased significant ly. Even if the barley meal was fed before the hay, excretion rates of all markers were similar. The digestibility of OM increased linearly (P <0.05) whereas that of NDF and ADF decreased (P <0.05). Although the MRTs increase d when grain was fed, the efficiency of fiber utilization decreased. Furthe r investigation on fibrolytic microbial ecosystem are required to explain t hese observations.