The effects of monensin on amino acid catabolizing bacteria isolated from the Boer goat rumen

When ruminants consume feed, as much as half of the amino acid nitrogen can be lost due to microbial degradation in the rumen. Hyper ammonia-producing bacteria (HAB) are primarily responsible for amino acid loss in sheep and cattle, and ionophores (e.g. monensin) are used to inhibit the HAB. Ionophores are sometimes included in the diets of meat goats, but the effects on caprine HAB have not been investigated. Five amino acid catabolizing bacteria were isolated from the rumina of Boer goats, which were consuming a supplement that contained monensin. Two of the isolates were most closely related to the bovine HAB, Peptostreptococcus anaerobius, but the other three were more closely related to Peptoniphilus indolicus. When the isolates were exposed to monensin, intracellular potassium was lost, and ammonia production was inhibited. However, the P. indolicus-like isolates demonstrated a greater capacity to overcome this inhibition in growth experiments. These results indicate that the monensin sensitivity of these bacteria can be variable, even when previous exposure to monensin occurred in the rumen environment. Published by Elsevier B.V.