Like melamine, cyanuric acid is also used to artificially increase the nitrogen content of the food (detected as protein in protein tests).
Perry Martos and colleagues in the Agriculture and Food Laboratory at Guelph’s Laboratory Services have found that melamine and cyanuric acid can react with one another to form crystals that may impair kidney function. Tests conducted at the University’s Animal Health Laboratory (AHL) and elsewhere have identified these crystal-like substances in the kidneys and urine of affected animals. The experiments conducted at the Agriculture and Food Laboratory showed that the chemical composition of the crystals that are formed when these two compounds interact matches the composition of urinary crystals removed from affected animals. Tests conducted at the University’s Laboratory and in the United States have identified the compounds as contaminants in gluten used to make a variety of pet food and treat products.
Interestingly enough, the analytical test for cyanuric acid is to precipitate it with Melamine, so it is not as if these guys “discovered” this reaction, as the press release seems to intimate. There is also speculation that the cyanuric acid was a metabolic byproduct of melamine from bacterial action, which is possible if the gluten was not stored correctly. It seems to me that Chinese manufacturers were using melamine or cyanuric acid to boost protein content for a while now. But it may have been only recently that they started adding both to the same food. The other possibility (and have you ever read the ingredients list in pet food, it takes a while!), is that one ingredient contained melamine, the other, cyanuric acid and when mixed…
Either way, neither of these compounds belong in pet food.