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This article was published in 1980
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A Condition Resembling Nitrite Poisoning in Pigs
J.M. Wilson, B.V.Sc. Veterinary Inspector, Tweed-Lismore
Introduction
The owner of a Lismore Piggery was purchasing store pigs from properties in the Dubbo and Forbes areas, and transporting them to his property where they were fed a diet of bakers' and greengrocers' wastes collected around Lismore City, together with buttermilk supplied from Norco Co-operative Dairy Factory thrice weekly, stored in large open vats on the piggery. The average number of store pigs on hand was 600, and they were turned off the property for slaughter as bacon.
The property was under frequent official surveillance for two reasons - firstly the type of diet supplied presented a constant risk of pigs being 'accidentally' fed on meat scraps, and secondly the poor quality of pigs purchased and the husbandry practiced predisposed to mortalities from enteric infections.
Between 16th and 18th June, 1976, 15 four months old store pigs died from a condition resembling nitrite poisoning.
History
Pigs were fed buttermilk at 9:30 am on 16.6.79. Two hours later all appeared normal. On checking the piggery at 4 pm. 10 were found dead, not involving any particular pen but scattered throughout the piggery. A cadaver was taken to the Regional Veterinary Laboratory at Wollongbar where necropsy showed chocolate discolouration of the blood and brown colouration of subcutaneous tissues, muscle, liver, lung and visceral fat. A diphenylamine test for nitrites/ nitrates carried out on stomach contents was positive.
The following day the pigs were kept under observation following feeding.
Three were soon to vomit within 15 minutes of feeding and died within an hour after exhibiting signs of respiratory distress. Another cadaver was transported to the Regional Veterinary laboratory. The post-mortem features of this animal closely resembled those of the previous submission - chocolate coloured blood, muscle, connective tissue and parenchymatous organs. The blood had clotted normally and it tended to become reddish after exposure to air. The diphenylamine test again gave a positive result for nitrites /nitrates, both on stomach contents and peritoneal fluid.
The following day (18.6.76) two more pigs died under similar circumstances so samples of buttermilk, drinking water and meal were tested for nitrites with a strong positive result in the case of buttermilk.
At this stage the owner elected to reduce the amount of buttermilk fed and no further mortalities occurred.
In the meanwhile, bacteriology carried out on different samples of buttermilk of different ages from different storage vats yielded mixed growth of organisms of no apparent significance.
Three collections of buttermilk were then made (24.6.76) The first, direct from the Norco factory storage, yielded a moderately positive reaction for nitrites/nitrates. The second, after 12 hours farm storage, gave a slightly positive reaction, while that samples after 24 hours farm storage was negative.
It could therefore be suspected that the methaemoglobinaemia associated mortality originated from some aspect of the manufacture or storage of buttermilk at factory level.
Discussion
Clarke & Clarke (1975) refer to mortalities from nitrite and nitrate poisoning when swill made with well water containing excess nitrate is fed. Nitrate poisoning has also been seen in domestic animals fed meat scraps where the meat has been pickled or cured using nitrites and/or nitrates. Nitrites are sometimes used as a preservative for whey.
Ultimately, it was learned that the butter factory had been having maintenance problems with a refrigeration unit and this resulted in the leakage of ammonia gas from the refrigerator into the buttermilk storage tank.
Conclusion
It appears likely that the ingestion of ammonium hydroxide by pigs produces death through methaemoglobinaemia in a similar manner to that caused by the ingestion of nitrites.
References
Clarke,e.g.C. & Clarke, Myra L. - Veterinary Toxicology, 1975 edition
Helwig, D.M. and Setchell, B.P., (1960) Aust. Vet. J. 36:1:14