Mode of Action of Penicillin in the Prevention of Uncomplicated Legume Bloat

Summary The study was conducted to determine whether increased intraruminal stable froth formation is clearly associated with an increased incidence of naturally occurring bloat and how penicillin is effective in preventing bloat and why its preventive effect is short-lived. Fistulated and nonfistulated dairy animals were grazed and stall-fed under carefully controlled conditions on bloat-producing and nonbloat-producing alfalfa during 1960 and 1961. A number of stall-fed animals received penicillin or served as controls. Over an entire bloat season, stable froth formation in the rumen was found to be significantly correlated with the bloat index ( r = 0.42). The coefficient of correlation between bloat incidence and gas production by the rumen microorganisms (as determined by a Warburg apparatus) was highly significant (0.65), showing that an unusually high rate of gas production is involved in the etiology of bloat. The administration of penicillin significantly lowered both stable froth production and gas production. It was concluded that penicillin exerts its shortlived bloat preventive effect by decreasing the rate of stable froth formation in the rumen through a reduction in the rate of fermentation.