Corn in the Rat Diet

Theresa Lee
From the RMCA web site, August 2002

Corn in the rat diet should be limited. Why? The other myco!

Mycotoxins, toxic metabolites produced by fungi, are common contaminants of grains and other food products. Aflatoxin and fumonisin, two of the most well known mycotoxins, are known animal carcinogens and are largely found as contaminants of corn.

Aflatoxin causes liver, kidney, and colon cancers in rats. The TD50 is the chronic dose-rate in mg/kg/day, which causes tumors in half of the population and is a measure of carcinogenic potency. The aflatoxin TD50 in rats is 0.0032 mg/kg/day. Assuming the daily food consumption of rats to be about 10g / 100g, this translates to aflatoxin levels of 32 ppb in the rat diet. Aflatoxin has also been classified as a known human carcinogen, and aflatoxin levels are therefore regulated by the FDA and USDA. Aflatoxin levels in human and pet foods may not exceed 20 ppb, and aflatoxin levels in other animal feeds may not exceed 300 ppb.

Rats are the species most sensitive to aflatoxin. Based on epidemiological studies, rats are estimated to be about 10,000 times more sensitive to the effects of aflatoxin than are humans. Thus, the FDA-set maximum allowable level of aflatoxin allowed in human and pet foods, 20 ppb, may not be set low enough to protect rats from the effects of aflatoxin.

Fumonisin causes liver cancer in rats. The fumonisin TD50 in rats is 1.16 mg/kg/day. Assuming the daily food consumption of rats to be about 10g / 100g, this translates to fumonisin levels of 11.6 ppm in the rat diet. It is unknown if fumonisin is a human carcinogen, and fumonisin levels are therefore not regulated. The FDA has set guidance levels for fumonisin levels in human foods and animal feeds on the order of ppm and 100's of ppm, respectively, but, again, these are only recommended levels and fumonisin levels are not regulated.

Aflatoxin is a common contaminant of corn and peanuts and their products, and fumonisin is a common contaminant of corn and corn products. In these foods, aflatoxin and fumonisin most likely occur at levels, which are carcinogenic to rats; so feeding a daily diet, which consisted only of these foods, would result in liver, kidney, and colon tumors in many of the rats. Feeding a daily diet limited in corn and peanuts and their products reduces aflatoxin and fumonisin levels and reduces associated tumor risks.


Action Levels for Aflatoxins

Guidance for Industry: Fumonisin Levels in Human Foods and Animal Feeds

Background Paper in Support of Fumonisin Levels in Animal Feed

Background Paper in Support of Fumonisin Levels in Corn and Corn Products Intended for Human Consumption

Carcinogenic Potency Database (CPDB)