Recently our SPCA Inspector Stephanie Fortuin was called out to a heartbreaking scene at a small farmers holding in Darling. She found 4 of 9 very ill horses who were seemingly poisoned. The vet, also present, had to euthanise 2 of the horses, 1 recovered after symptomatic treatment. The 4th horse had died before there could be any intervention.
Inspector Fortuin was adamant that the cause of this horrifying scene need to be investigated. She summarily decided to load the 4th horse into her bakkie and drive it to the State Vet in Elsenburg, Stellenbosch for an autopsy. The heart broken owner also needed some answers.
The report that came back declared the cause of death as phosphine poisoning. The horses had died as a result of being fed grain siftings (or sweepings) which are the cheaper remains that are not sold for human consumption and found at the bottom of silos.
We now understand that aluminium phosphide is used as a fumigant in grain silos for the control of insects such as grain weevils. Small remnants of aluminium phosphide are sifted out of the main body of grain and become concentrated in the siftings and may reach toxic levels.
In animals phosphine primarily affects the central nervous system (causing hypersensitivity, convulsions and coma), the gastrointestinal tract (causing vomiting, colic and tympany) and the respiratory tract (causing polypnoea and dyspnea). The mechanism of action is unknown.
The report on phosphine poisoning sent to us by the state vet said the following:
It would appear that silo operators and livestock farmers are unaware of the fact that siftings of fumigated grain may still be toxic, for 14 days or even longer, after being released from the silo and aerated. (However, once fumigated grain is aerated, which liberates trapped phosphine PH3gas, it is completely safe for human or animal consumption.) The danger of using grain siftings from fumigated cereals should be clearly stated on the instructions and package inserts accompanying the various fumigation products. There should also be a warning that grain siftings should be moistened with water and allowed to dry out before it can be safely used as animal feed. This information should be made available to all grain handling and storing Agri businesses in South Africa, so that they can warn clients buying siftings. It should also be emphasised during the training of silo operators.
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