Nitrogen dioxide (silo gas) poisoning in pigs

Toxic silo gases are a potential danger to livestock housed in close proximity to silos. On the fourth day of ensiling, five fattening pigs were found dead in a pen adjoining a grass silo. Post mortem examination revealed extensive lung damage and methaemoglobinaemia. A dense reddish-brown gas was concentrated at floor level to a height of 1 m in the pen and had diffused into adjoining pens, where dry and suckling sows and litters were showing signs of respiratory distress and weakness. The gas was identified as a mixture of nitrogen dioxide and dinitrogen tetroxide. These gases may be produced in the early stages of silage making. In this case, they had accumulated in a slurry channel below the silo and leaked through an adjoining wall into the piggery. The production and toxicological effects of silo gases are discussed.