Feeding and microbial disorders in horses: 1-effects of an abrupt incorporation of two levels of barley in a hay diet on microbial profile and activities

Cecal and colonic fluid samples collected from three ponies were analyzed to determine the effects of an abrupt incorporation of barley in a hay diet on their microbial and biochemical characteristics. Three diets based on meadow hay and rolled barley were tested in a 3×3 Latin square experiment: 100% hay (100:0, 114 gDM/KgBW0.75/day), 70% hay—30% barley (70:30, 69gDM/KgBW0.75/day) and 50% hay—50% barley (50:50, 58gDM/KgBW0.75/day). Enumeration of total anaerobic and aeroanaerobic bacteria, lactate-utilizing and cellulolytic bacteria, lactobacilli and streptococci, as well as pH, lactate and VFA concentrations, were determined before and five hours and 29 hours after the abrupt incorporation of barley in the hay diet. Whatever the amount of barley incorporated, an increase of total anaerobic bacteria, lactobacilli and streptococci, in the cecum and in the colon, was reported 29 hours after the changing of diet. Lactateutilizing and cellulolytic bacteria were not significantly modified five hours and 29 hours after the ingestion of a new diet. However a decrease of [(acetate+butyrate)/propionate] ratio was registered while lactate concentration increased although pH remained fairly constant through the changing of diet. The colon appeared to be the main site affected by the abrupt incorporation of readily fermentable carbohydrates in the diet. Thus, this section of the digestive tract needs further exploration to establish the linkage between the changes of the ecosystem as reported here, and the apparition of intestinal disorders.