Microbial characteristics of ruminal fluid from feedlot bloat beef cattle

Rumen samples from bloating steers had volatile fatty acids (VFA) concentrations high in acetate and low in propionate so that the acetate/ propionate ratio was consistently higher in bloating animals than in healthy ones. The ruminal pH values in bloated steers were compatible with those in healthy steers. Ammonia concentrations were higher in bloated steers than in healthy ones. There were no essential differences in the rates of gas production in vitro by rumen fluid between bloated and healthy steers. The total count and generic composition of rumen ciliates were similar in all steers and not likely to correlate with bloat. In contrast, although the total counts of bacteria in bloated steers were of the same order as those from healthy steers, the constitution of microflora was greatly affected by the development of bloat: gram-negative cocci (0.3-1.0μm), gram-positive cocci (0.5-1.1μm) and gram-positive small rods {(0.45-0.65μm)×(0.65-1.2μm)} increased, while gram-negative small rods {(0.35-0.7μm)×(0.9-2.0μm)} decreased in bloating steers.