By the time the cause of the illness and deaths was identified, melamine and cyanuric acid contaminated ingredients resulted in the adulteration of millions of individual servings of pet food. Checks to ensure the safety of the imported ingredients had not been conducted by the importer or by the pet food manufacturers that incorporated the ingredients into pet food.
During the investigation, FDA determined that leftovers from the production of pet food (commonly called fines) and salvaged, finished pet food products were routinely used in the production of feed for some food-producing animals (e.g., swine and poultry). It was ultimately discovered that some of these fines and salvaged pet food were adulterated with melamine (and other triazine analogs). Urine from swine (that were being raised for human food consumption) that had eaten this contaminated food was tested and found to contain melamine. This discovery resulted in the holding of animals before their marketing for human food in order to provide time for the U.S. government to conduct a risk assessment to ensure the safety of the meat for human consumption. It was ultimately determined there was no risk to human health from eating meat from these animals due to the small amounts of contaminants in the animal feed eaten.
The contaminated wheat gluten was also used in the manufacture of fish food used in fish hatcheries for food-producing fish. As a result, there was a recall of the affected fish food. These situations with food-producing animals emphasized the link between adulterated animal food (and ingredients) and the potential for adverse effects on human health.
The melamine incident underscored the difficulty in tracing an adulterated ingredient that has been used in a large number of food products. The list of recalled animal foods was constantly updated for multiple weeks after the initial identification of the adulterated ingredients as the distribution of those ingredients was traced. Pet food companies who thought their pet foods were safe because their formulations did not included the use of wheat gluten or rice protein concentrate were surprised to find some of their products were indeed adulterated with the melamine and cyanuric acid. An FDA investigation revealed that a contracted pet food manufacturer was substituting rice protein concentrate for other sources of protein called for in these formulations without contacting the parent company.
Additional incidents of animal food contamination not discovered until after the food was distributed include the detection of dioxin in feed. Dioxin has been linked to adverse health effects in humans, such as cancer, immune suppression, and reproductive or developmental effects. Dioxin is a concern in food-producing animals because human dioxin exposure in the United States comes primarily from the consumption of animal products. In 1997, the USDA'sFood Safety and Inspection Service, through their dioxin sampling survey, identified dioxins in poultry tissue. Through a multi-agency investigation, the FDA traced this contamination to high levels of dioxins present in an anti-caking agent (ball clay) used in animal food. That same year, FDA issued a statement to users of ball clay products in animal feed requesting those companies to cease the use of ball clay products in animal feeds and feed ingredients (Ref. 18). In 2002, a foreign government identified high dioxin levels in a mineral product intended for animal food imported from the United States (Ref. 19). The source of the dioxin was related to the high temperature used in the mineral manufacturing process. In 2003, another dioxin incident in minerals was identified as a result of an FDA food sampling assignment. In this case, the mineral premix manufacturer purchased a trace mineral that was a by-product of a metal smelting process (Ref. 20). Internationally, in 1999, animal feed contaminated with dioxin and polychlorinated biphenyls in Belgium resulted in animal and human exposure in Europe. The Belgium government estimated the economic impact of the dioxin crisis cost $493 million, of which $106 million was lost in the swine industry alone. The total cost is much greater when factoring in the impact that occurred to the animal and human food industries in European countries that imported contaminated animal food (livestock feed) or human food from Belgium (Ref. 21). In 2009, a dioxin incident occurred in Ireland involving swine feed that resulted in a global recall of Irish pork. This incident resulted in the Irish government providing [Euro] 200 million ($266 million) compensation packages for the Irish pork industry due to their economic losses (Ref. 22). These incidents raised public awareness of the problem of dioxin contamination in animal food.