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 dADF) were measured in the entire digestive tract of six ponies to determine the effects of the dietary hay:grain ratio on the efficiency of fiber digestion. Three diets based on chopped meadow hay and rolled barley were tested in a 3×3 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 (50:50, 58gDM/KgBW^0.75/day). Particles markers (Europium for hay and Ytterbium for barley) and a solute marker (Cr-EDTA) were used for passage rate measurements. As the proportion of barley in the diet increased, DM intake decreased and mean retention time (MRT) of all markers increased significantly. 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 increased when grain was fed, the efficiency of fiber utilization decreased. Further investigation on fibrolytic microbial ecosystem are required to explain these observations.