Cats fed dry cat food that had been irradiated (Orijen brand from Champion Petfoods Ltd of Canada) suffered forms of paralysis and subsequent death. Many were euthanized.1
It does appear that irradiation of the food caused the illness:
"Previously published data and strong circumstantial evidence in this outbreak suggest that single-dose gamma irradiation of dry pet food at high levels (>36.3 kGy) is associated with the development of leucoencephalopathy in cats. We suggest that food irradiated at high levels should not be fed to cats as it poses a significant risk of severe neurological disease.How consumption of irradiated food may cause neurological damage:
Orijen was subject to a total gamma irradiation dose >50 kGy on entry to Australia."
"Irradiation results in the production of ions and free radicals, including high-energy oxygen radicals, that are used to kill or damage pathogenic organisms in food. Irradiation doses of foods for human consumption normally range from less than 1 up to 10 kGy. Larger doses (30 kGy) have been approved for dried herbs, spices and dehydrated vegetables. Oxygen radicals produced by irradiation will also cause the formation of lipid oxides by directly reacting with membrane lipids and other lipids in foods, and some foods such as fatty fish and meat are not considered good candidates for irradiation. Irradiation also induces chemical changes in carbohydrates and proteins by the action of hydroxyl radicals and hydrated electrons generated from water molecules to produce radiolytic products. These products are also generated in cooking or pasteurisation."So, the dose of radiation was thought to be significant in this case, but the risk from chronic, low-dose exposure wasn't ruled out:
"However, the mechanism by which changes induced in foods then result in damage to the white matter of the spinal cord and brain is not clear. Whether a single insult to the CNS results in on-going damage or whether the damage is the result of cumulative or repeated insult remains speculative."Maybe this is something just unique to cats? I know the USDA/FSIS is considering (and the American Meat Institute is endorsing) the use of radiation on beef to reduce risk from foodborne pathogens. Some ground beef on the market is already irradiated.
I wonder what happened to all that recalled cat and dog food, in so much as "the fate of salvaged pet food ... it gets turned into feed for pigs, poultry, and farmed fish," according to Marion Nestle.
Rundown from Felipedia: Effect Of Gamma-Irradiated Commercial Dry Pet Food In Cats