Two chemicals found in recalled pet food during spring 2007 are relatively harmless alone but, if combined, create a deadly mix when consumed by cats, report researchers at the University of California, Davis.

A pilot study, led by veterinary toxicologist Birgit Puschner and colleagues at the California Animal Health and Food Safety Laboratory in the UC Davis School of Veterinary Medicine, found that cats that were fed pet food spiked with both melamine and cyanuric acid quickly experienced acute kidney failure. Cats that received food containing only one or the other of those two chemicals experienced no ill effects.

Results of the study, believed to be the first report on the combined effects of melamine and cyanuric acid in any animal species, are published in the November issue of the Journal of Veterinary Diagnostic Investigation.

"The results of this study demonstrate that a single oral exposure of cats to melamine and cyanuric acid can result in acute kidney failure," said Puschner. "The study also provides information that will help veterinarians better diagnose the causes of kidney failure in cats."

Melamine, a chemical mainly used in production of certain resins and fertilizers, was the prime suspect during the investigation into the contaminated pet food episode of 2007, which resulted in the deaths of dozens of dogs and cats throughout the United States. Investigators suspected that melamine might have been added to boost the apparent nitrogen content of the pet foods. Researchers were puzzled, however, because melamine was considered to be relatively nontoxic.

Also surprising was the discovery of cyanuric acid in the recalled pet food. Cyanuric acid, which is structurally related to melamine, is commonly used in swimming pools and hot tubs to slow the breakdown of chlorine in the water.

Scientists suspected that both melamine and cyanuric acid played a role in the illnesses of animals that ate the recalled pet food; however, there was no information on the toxicity of the two chemicals in combination.

During the pilot study, Puschner and colleagues found that the cats that received both melamine and cyanuric acid developed fan-shaped crystals in their urinary tracts. Such crystals were not normally observed in healthy cats. Those cats also experienced extensive damage to their kidneys within 12 hours after eating the spiked food.

The research team suggests that, in order to provide more extensive data for a risk assessment of contaminated food, further studies are needed to determine the lowest dose of melamine and cyanuric acid that can cause kidney failure in cats.