Pony Cecum vs. Steer Rumen: The Effect of Oats and Hay on the Microbial Ecosystem

Two 4 × 4 latin square design studies were conducted to determine the effect of diet on the microbial population of the equine cecum and steer rumen. The animals were fed timothy or clover hay with or without oats as 25% of the diet at 2% of body weight. Increases (P<.05) in total and viable bacteria/ml ingesta and DNA occurred when oats were fed to the ponies. These differences did not occur in the steers (P>.05). Rods, Gram-negative and positive, predominated in the Gram-smear counts of both ponies and steers and the isolated strains from the ponies. Of the presumptively identifiable isolated strains, Streptococcus bovis and Bacteroides species were the most predominant. Diet did however affect the proportion of protozoal types in the ponies. When oats were fed, Blephacorys uncinata increased (P<.01) and when timothy plus or minus oats were fed, Cycloposthium bipalmatum increased (P<.05). No differences (P>.05) in total protozoa/ml ingesta were found in either the ponies or the steers. Clover hay plus or minus oats increased total VFA concentration in both the ponies and the steers. In both species acetate concentration increased (P<.05) when clover hay was fed. A relatively large percentage of equine cecal bacteria (19.7%), including many different types, were proteolytic. This suggests that cecal bacteria may have the potential to provide nitrogen to the equine. Cellulolytic bacteria numbers per gram ingesta were similar in the ponies' cecum and steers' rumen, whether or not oats were included in the diet.