Microbial and fermentation changes in the rumen in
monensin- and
lasalocid-fed cattle grazing bloat-provocative alfalfa pasture were studied using genetically bloat-susceptible, ruminally-cannulated adult cattle.
Monensin at .66 and .99 mg/kg
body weight daily reduced the severity of legume bloat by 41 and 73%, respectively. The same doses of
lasalocid reduced bloat by 25 and 12%. Comparison of ruminal contents from animals before treatment with ruminal contents from
antibiotic-treated animals showed no differences in pH,
ammonia, soluble N, soluble
carbohydrate,
ethanol-precipitable slime and anaerobic bacterial counts.
Monensin treatment decreased protozoal numbers and microbial activity, as evidenced by lower gas production from in vitro fermentation of ground alfalfa hay when compared to pretreatment.
Lasalocid had no effect on protozoal counts and in vitro gas production. Addition of
monensin or
lasalocid (12 micrograms/ml) to in vitro fermentation of chopped, fresh alfalfa reduced microbial activity as evidenced by higher soluble N, lower
ammonia concentration and decreased gas production.
Monensin reduced the amount of
ethanol-precipitable slime and protozoal numbers. Reduction in the severity of bloat when
monensin was fed appears to be due to decreased protozoal numbers, which resulted in decreased gas production.
Lasalocid did not reduce legume bloat because of its minimal effect on the ruminal protozoa.