Swine enzootic pneumonia: age susceptibility and treatment schemata.

Pigs were found to be susceptible to Mycoplasma hyopneumoniae-induced swine enzootic pneumonia (SEP) when four hours old. Chlortetracycline was incapable of preventing transmission of SEP from infected pigs on the drug to susceptible, untreated pigs. When continuous medication was started at one or two weeks postinoculation, chlortetracycline partially or completely inhibited formation of SEP lesions but did not clear M. hyopneumoniae from inoculated pigs. Chlortetracycline administered orally was capable of completely suppressing the formation of SEP lesions in inoculated pigs if given prophylactically and if milk was withheld for several hours after each treatment; lesion suppression was incomplete if milk was given ad libitum. In either case treated animals remained infected with M. hyopneumoniae.