Acclimation of replacement gilts to Mycoplasma hyopneumoniae: a case study of fogging with an aerosol inoculum

Context Mycoplasma hyopneumoniae causes enzootic pneumonia, predisposing pigs to infections with other respiratory pathogens. The main control measure is to reduce piglet exposure at lactation, which can be achieved by gilts' acclimation prior to their entrance to the farms. One of the acclimation strategies is aerosol exposure with a positive inoculum by using a fogger. However, studies on its efficacy in gilts and their litters are lacking in the literature.Aim The aim of this case study was to assess the efficacy fogging with a positive inoculum of M. hyopneumoniae to expose negative gilts in an acclimation program. Moreover, the infection dynamics of M. hyopneumoniae were assessed in their piglets from lactation to slaughter.Methods The trial was performed in two phases. In Phase 1, a total of 34 and 107 gilts was selected from Farms A and B respectively, and then exposed to the inoculum through a fogger. In Phase 2, a subsample of 74 gilts from Farm B was followed to their first farrowing and 263 piglets born to those gilts were sampled from 15 to 170 days of age, and at slaughter, lung lesions were evaluated.Key results In Phase 1, the prevalence of positive gilts at 28 days post-exposure (dpe) was 100% and 98.1% in Farms A and B respectively. In Phase 2, 10.8% of gilts remained positive at 180 dpe and 0.8% of piglets were positive at 15 days of age (day) and 28.1% at 60 days, suggesting a possible vertical transmission.Conclusion The use of fogging with a lung homogenate positive for M. hyopneumoniae successfully acclimated negative gilts. However, it did not avoid the presence of positive gilts at farrowing and the detection of the bacterium in their progeny by polymerase chain reaction.Implications The exposure of gilts to M. hyopneumoniae at 150 days of age was successfully achieved by fogging. However, consideration should be given to exposing replacement gilts of a younger age in order to reduce the odds of detecting positive gilts at first farrowing.