Survey of chemical compounds tested in vitro against rumen protozoa for possible control of bloat.

Over 170 chemical agents were screened for antiprotozoal action in bovine ruminal fluid. Compounds were tested at 0.1 and 0.05% concentrations. Tested compounds included inorganic compounds, antibiotics, biocides, neuromuscular agents, arsenicals, plant and animal hormones, antimalarials, surface-active agents, anthelmintics, and many others. The most active compounds were cupric sulfate, nickel sulfate, nitrofurazone, hydrogen peroxide, dodecyl sodium sulfate, pelargonic acid, iodoacetic acid, 1-diethylaminoethylamino-4-methylthiaxanthrone, sodium arsanilate, sodium arsenate, bismuth glycolyl arsanilate, 1-beta-hydroxyethyl-2-methyl-5-nitroimidazole, and p-nitroaniline. Copper ion was not particularly effective against entodinia; nickel ion had no effect on holotrichs. Hydrogen peroxide and iodoacetic acid were effective at a concentration of 0.005%. Anionic surface-active agents were very effective, especially long-chain sulfates and phosphates. These antiprotozoal agents warrant further in vivo studies for possible use in treating or curing bloat in ruminants.