Investigation of possible aetiological/triggering factors in porcine ear necrosis syndrome at a farrow-to-feeder pig system.

At a commercial farrow-to-feeder pig system with 2,100 sows in Serbia, lesions resembling porcine ear necrosis syndrome were observed in 80% of the weaned pigs at 45-50 days of age. Pathomorphological examinations were carried out on 10 pigs that had been found dead. The gross lesions ranged from mild, superficial dermatitis to severe, deep inflammation with exudation, ulceration and necrosis. Histopathological examination revealed erosive and ulcerative dermatitis of the pinna with neutrophilic and lymphocytic infiltration and bacterial colonies in the crusts. Staphylococcus aureus (MRSA strain), Staphylococcus hyicus and Streptococcus group C were cultivated from eight, S. hyicus from two ear tissue scraping samples. All 10 samples were positive for treponemes and phylogenetic analysis of two polymerase chain reaction products confirmed the relationship to Treponema (T.) medium/vincentii and Treponema pedis. Treponemes were also detected in seven oral swabs that were analysed to obtain evidence of the transmission of this bacterium by ear biting. The contribution of non-infectious factors to this misbehaviour could not be ruled out as the crude protein concentration of the feed was inappropriate and the climate of the pig house was suboptimal. The concentrations of selected mycotoxins in the feed were not elevated. However, the contribution of both infectious and non-infectious factors to the onset of disease was most probable.