Aspergillus flavus and A. parasiticus are common in most soils and are usually involved in decay of plant materials. They commonly cause stored grams to heat and decay and, under certain conditions, invade grain in the field. The problem is serious in subtropical and tropical regions of the world where cereals, peanuts, corn, and copra are important in the human diet.
Aflatoxins B1, B2, G1, and G2 are produced by A. flavus and A. parasiticus in grains in both field and storage. Infection is most common after the kernels have been damaged by insects, birds, mites, hail, early frost, heat and drought stress, windstorms, and other unfavorable weather. Aflatoxins Ml and M2 are found in milk from animals fed aflatoxin-contaminated feeds. The presence of A. flavus or A. parasiticus in a given feed sample does not imply that the feed is unwholesome and will contain high levels of aflatoxin. Aflatoxin persists under extreme environmental conditions and is even relatively heat stable at temperatures above 212 degrees F, the boiling point of water. Roasting, ammoniation at ambient temperatures, and some microbial treatments may sharply reduce but not eliminate the aflatoxin content. Ammoniation has been shown to be most effective in reducing aflatoxin levels.
Currently, these treatments have limited application, with roasting being the least effective. Pelletizing feeds may eliminate fungi present in the stock but not reduce or eliminate aflatoxin present in any of the ingredients.
Recently, the addition of binding agents such as hydrated sodium calcium aluminosilicate (HSCAS) and bentonite clays to corn has been shown to decrease the effects of aflatoxin when fed to swine. These compounds probably work by nonspecific binding to the mycotoxin and reducing the passage time through the gut. Although not specifically approved for this purpose, various products that have this ability are approved as binding or anti-caking agents.
Control swine fed aflatoxin-contaminated corn had significantly poorer average daily gain and feed efficiency than those fed the same contaminated corn mixed with HSCAS. NovaSil was shown to be effective at either 5 or 10 pounds of compound per ton of aflatoxin-contaminated feed. The current cost of including this product in feed at this level would be $3 to $4 per ton of feed.
Another binding agent that has been shown to be effective in reducing the effects of aflatoxin in corn are the clays, Volclay or FD-181.2 In a Virginia study these products, added to aflatoxin-contaminated corn, increased average daily gain and feed efficiency to levels similar to those of control pigs. The products were included in the feed at 10 pounds per ton. At that level the cost of including these products would be approximately $1 per ton of feed.
All animal species are susceptible to aflatoxicosis, although sensitivity varies considerably from species to species. For example, birds, fish, dogs, and swine appear to be more susceptible than mature cattle. In poultry, besides fatty liver and kidney disorders, leg and bone problems can develop as well as outbreaks of coccidiosis. Aflatoxins may cause vaccines to fail, increase the birds’ susceptibility to disease, and result in suppression of the natural immunity to infection. The animals become susceptible to infection by bacteria such as Salmonella and to various viruses and other infectious agents commonly found around the farm yard, feedlot, or poultry house that normal healthy animals ward off. Decreased blood clotting results in a greater downgrading and condemnation of the birds because of massive bleeding and bruises. .Less carcass pigmentation is exhibited and egg yolks are paler. The hatchability of eggs can drop, and reduced production may be noted as well as smaller eggs with shell problems. Growth is restricted and mortality increases, especially during the growing period.
Regular or occasional consumption by farm animals of feed containing aflatoxin in the range of less than 100 ppb to a few hundred parts per million (ppm) results in decreased feed consumption, poor feed conversion, stunting, and decreased flesh growth. Decreased productivity may be accompanied by damage to the liver, hemorrhaging into the muscles or body cavities, and suppression of natural immunity to parasites and pathogens always present in the environment. Once the damage has been done, the animals will not fully recover, even if returned to a toxin-free ration.
Aflatoxin is present in the spores of A. flavus, which sometimes are produced in great abundance on the ears of fungus-infected corn. When corn is combined and unloaded at elevators or other transfer points, it generates considerable dust, and some of this dust may contain aflatoxin. Dust collected near a combine in Georgia in 1980 contained from 2,030 to 41,200 ppb of aflatoxin. The aflatoxin content of the dust at the elevator receiving this corn ranged from 621 to 1,480 ppb.
Dust masks should always be worn when handling obviously moldy grain. Inhaling aflatoxin-contaminated dust is presumed to be a health hazard. Grain handlers have more respiratory problems than the general population. “Farmer’s lung” is a disease that afflicts grain handlers and is frequently associated with skin irritation, fever, wheezing, breathlessness, cough, and ulcers. Farmer’s lung is thought to be caused by an allergic reaction to fungal spores and other material in grain dust. Pulmonary mycotoxicosis is a disease that occurs in farmers when they inhale large amounts of grain dust containing fungal hyphae and spores. This latter disease is a direct effect of the fungal toxins, not an allergic reaction.
Grain invaded by Aspergillus species is highly friable, therefore great care should be taken when feeding grain screenings. Broken grains often have very high levels of aflatoxin concentration.