Acute nitrite toxicosis in fattening pigs. A case report

摘要

On three days over a period of ten months, high spontaneous mortality (31%, 61%, 17%) occurred in pigs (aged 4 to 6.5 months) of a fattening unit. In the first two cases, pigs were necropsied about 36 hours postmortem, but the findings were nonspecific. Feed toxicosis, ventilation failure or gas toxicosis were suspected in the first cases, but none of these could be confirmed as the cause of the high mortality. Only in the third case was immediate clinical and postmortem examination possible. The chocolate colour of the blood and the increased level of methaemoglobin in pigs with clinical signs led to the suspicion of nitrite toxicosis. The detection of nitrite in the stomach contents (600 mg/kg) and swill (800 mg/kg) confirmed the diagnosis. Thereflux of rinsing water from a so-called biofilter could be identified as the source of nitrite. The filtering plant is used to oxidize ammonia in the exhaled air into nitrite and nitrate and ultimately into gaseous nitrogen (denitrification). The filterconsists of a layer of volcanic stones which are colonized by nitrified bacteria. As the filter is sprayed continuously with water, the nitrite concentration in the rinsing water is high, about 2000 mg/litre. Drinking water is added to maintain the rinsing water cycle. During maintenance the drinking water pump was turned off while the magnetic valve which separates the two water lines remained open, causing the reflux of rinsing water in the drinking water line and thus the poisoning of the pigs.