Effectiveness of doxycycline in the prevention of an experimental infection with Actinobacillus pleuropneumoniae in pigs

The effectiveness of medication with doxycycline in feed in the control of pleuropneumonia in pigs was tested using an Actinobacillus pleuropneumoniae serotype 1 aerosol challenge model. Two groups of 10 animals were used for the challenge, a 'medicated group' and an 'unmedicated group'. A third gro up of four animals was used as a 'control group', Pigs from the medicated g roup were provided with feed containing 250 p.p.m. doxycycline (HIPRAMIS/DO XI) for 8 consecutive days and were challenged on the fifth day of treatmen t. No clinical signs were observed in pigs from the 'control group'. Four a nimals from the 'unmedicated group' died within the first 48 h after challe nge with clinical and lesional evidence of an acute form of pleuropneumonia . Clinical signs of animals surviving the first 48 h were progressively les s severe and showed lesions similar to those described for subacute-chronic forms of the disease. However, only one animal from the 'medicated group' showed clinical signs of a chronic form of pleuropneumonia. Reisolation of A. pleuropneumoniae was more evident from lung tissues of animals fed the d oxycycline-free feed (70%), coinciding with the presence of both acute and subacute lesions. However, the micro-organism could be reisolated from only one animal which belonged to the 'medicated group'. It is concluded that t he treatment of pigs with 250 p.p.m, doxycycline (HIPRAMIX/DOXI) prevents d isease caused by A. pleuropneumoniae.