Experimental infections with Actinobacillus pleuropneumoniae in pigs - II.Comparison of antibiotics for oral strategic treatment

The present study was aimed at scrutinizing the efficacy of oral antimicrob ial treatments at experimental challenge using a strain of Actinobacillus p leuropneumoniae serotype known to cause severe disease. SPF pigs aged 10 we eks were infected intranasally and the antimicrobial treatments were initia ted 5 h prior to that exposure. Several antimicrobial drugs, as well as the length of the treatment period, were elucidated. The outcome of the challe nge was monitored by registration of clinical symptoms, weight gains and th e development of serum antibodies to A pleuropneumoniae. At necropsy, the m agnitude of pathological lesions in the respiratory tract and the rate of r eisolation of the infective strain were recorded. Animals that became disea sed displayed a decreased growth rate caused, to a large ext ent, by a redu ced feed intake. The performance with respect to daily weight gain and feed conversion corresponded well with the clinical signs developed and serolog ic reactions, as well as with the findings made at necropsy. The results ob tained among pigs treated with enrofloxacin, but also with florfenicol or c hlortetracycline, were superior to those of pigs treated with penicillin, t iamulin or tilmicosin. A positive effect was obtained using a strategic in-feed medication against infection with A. pleuropneumoniae. Provided that the drug used is effecti ve against the target microbe, initiating treatment prior to infection appe ared to be more important than the length of the treatment. It should, howe ver, be remembered that A. pleuropneumoniae was reisolated from all but one medicated group following an experimental challenge given after initiating the medication. Consequently medical treatment as described did not eradic ate the microbe.