title: Monensin-resistant bacteria in the rumens of calves on monensin-containing and unmedicated diets.
abstract: Total and monensin-resistant anaerobic bacterial populations and volatile fatty acid concentrations were examined in the rumens of steers fed monensin-containing (33 mg/kg) and unmedicated diets. Total anaerobic counts on a habitat-simulating medium ranged from 7.1 X 10(8) to 7.1 X 10(9) CFU/g of rumen ingesta and were not significantly different in animals fed the two diets. The mean percentage of the anaerobic population resistant to monensin (10 micrograms/ml) was significantly greater in animals receiving the monensin-supplemented diet for 33 days than in those receiving the unmedicated diet (63.6 and 32.8%, respectively). Treatment group differences in monensin resistance tended to develop later than characteristic differences in acetate/propionate ratios. Relative proportions of resistant organisms in monensin-fed animals remained significantly greater for at least 18 days after monensin was deleted from the ration, whereas acetate/propionate ratios increased to values comparable to those in the control within 10 days. These data suggest that monensin-resistant bacteria may be present in greater numbers in the rumens of animals fed monensin-supplemented diets. However, greater proportions of monensin-resistant organisms were not necessarily associated with altered fermentation patterns.
mesh_terms: D000693:Anaerobiosis; D000818:Animals; D001419:Bacteria / Q000187:drug effects* / Q000378:metabolism; D002417:Cattle / Q000382:microbiology*; D004032:Diet; D004352:Drug Resistance, Microbial; D005232:Fatty Acids, Volatile / Q000378:metabolism; D005260:Female; D005663:Furans / Q000494:pharmacology*; D008985:Monensin / Q000008:administration & dosage / Q000494:pharmacology*; D012417:Rumen / Q000382:microbiology*
chemical_list: D005232:Fatty Acids, Volatile; D005663:Furans; D008985:Monensin