Clinical Effects of Aflatoxicosis

         Aflatoxicosis is a disease caused by the consumption of aflatoxins, and the effects are dependent on the species, age, and condition of the animals involved, the amount of aflatoxin consumed, and the length of exposure. Aflatoxin B1 is one of the most potent naturally occurring animal carcinogens. Aflatoxicosis has varying negative effects on animal health depending on the species, and aflatoxin has been implicated in cancer and other diseases in humans.

---

 
Beef Cattle

Aflatoxin is the most common mycotoxin known to affect beef cattle, although the problems are usually less critical than with poultry or swine. Calves are more sensitive to feed contamination than mature cattle, with pregnant or growing cattle intermediate in susceptibility. Early indications of aflatoxin toxicity include reduced feed intake followed by reduced weight gain or weight loss. Often there is reduced feed efficiency, increased susceptibility to stress, and decreased reproductive performance. Chronic aflatoxicosis is characterized by unthriftiness, anorexia, prolapse of the rectum, liver and kidney damage, depression of the immune system, and edema in the abdominal cavity. Caution and good judgement should be exercised when using feed containing as little as 60 - 100 ppb aflatoxin. These feeds, fed over an extended period, may depress performance in cattle . Chronic symptoms of aflatoxicosis can result from the continued intake of 700 - 1000 ppb of aflatoxin in feed of 450-pound cattle. Death of steers has been reported from an intake of 1000 ppb of aflatoxin in feed during a 59-day trial. Once damage has been done, the animals will not fully recover, even if returned to a toxin-free feed ration, however, a change to a clean uncontaminated, medium- to high-energy protein diet may improve growth rate and help animals recover from aflatoxicosis. A broad-spectrum antibiotic at treatment levels helps prevent secondary infections. Other types of stress should be avoided.


[Top of Page]

 
Dairy Cattle

Aflatoxin is of major concern to dairymen. Aflatoxin-contaminated feed not only negatively affects the cows health and performance as mentioned in the section on beef cattle, but it creates serious risk of aflatoxin residues in the milk. Aflatoxin is secreted into the milk in the form of aflatoxin M1 with residues approximately equal to 1 to 2 percent of the dietary level. Since aflatoxins also affect humans, a maximum level of 0.5 ppb of the aflatoxin is permitted in bulk tank milk. Generally, levels of 50 ppb or greater aflatoxin in the feed produce levels over 0.5 ppb in the milk. Once the contaminated feed is removed, aflatoxin levels in the milk will disappear in 48 to 72 hours.


[Top of Page]

 
Poultry

Aflatoxin affects all poultry species. Young poultry, especially ducks and turkeys, are very susceptible to aflatoxicosis. Generally, immature, growing poultry should not receive more than 20 ppb aflatoxin in the diet. However, feeding levels lower than 20 ppb may still reduce their resistance to disease, decrease their ability to withstand stress and bruising, and generally make them unthrifty. Laying hens usually can tolerate higher levels of aflatoxin than young birds, but aflatoxin levels still should be less than 100 ppb. Aflatoxicosis can reduce the birds’ ability to tolerate stress and other diseases by inhibiting the natural immune system. Stunted growth, increased mortality, reduced egg size and production, liver and kidney disorders, leg and bone problems, suppression of the immune system with increased susceptibility to infections such as Salmonella are common symptoms of aflatoxicosis in poultry. Decreased blood clotting results in greater downgrading and rejection of birds due to massive bleeding and bruises.


[Top of Page]

 
Swine

Swine are sensitive to aflatoxin, especially nursing or nursery-age swine. Generally, aflatoxin consumption primarily causes liver damage and can result in reductions in feed intake and growth performance. Aflatoxin levels of 100 to 400 ppb cause reduced growth rate and lower feed efficiency. This level of aflatoxin affects breeding stock, unweaned nursery, and growing pigs more than finishing swine (greater than 100 pounds). It is extremely important to keep toxin exposure to breeding swine to a minimum. Aflatoxin levels of 400 to 800 ppb has caused liver damage, bleeding disorders, immune system suppression, abortions, and death.


[Top of Page]

 
Sheep and Goats

Sheep and goats are affected by aflatoxin like other ruminants. Aflatoxicosis causes liver damage, kidney damage, anemia, and other symptoms similar to those found in cattle. Early symptoms may include depression, loss of appetite, weakness and slow movement.


[Top of Page]

 
Horses

Although the effects of various mycotoxins on horses are not as well documented in scientific literature as for some other animals, field situations suggest that mycotoxin problems are significant. Horses, which are non-ruminants, may be more susceptible to mycotoxins than ruminants, since nutrient absorption occurs prior to fermentative digestion in the horse compared to ruminants in which absorption occurs after fermentative digestion. Mycotoxins have been implicated in causing colic, neurological disorders, paralysis, hypersensitivity, organ deterioration, reduced growth rate, poor feed efficiency, impaired fertility, and death. Due to the lack of conclusive scientific research concerning the levels of various mycotoxins tolerated by the horse, emphasis should be placed on feeding mycotoxin-free grain and forage to horses. Based on field observations, it has been suggested that the maximum aflatoxin level for mature, non-breeding horses should not exceed 50 ppb, and that growing horses (less than 2 years old), breeding horses, and work horses, should receive only aflatoxin-free rations.


[Top of Page]

 
Humans

The effect of aflatoxins on human health is difficult to assess. Reports in the scientific literature associate aflatoxin with acute human poisoning. Acute liver damage can occur in humans from ingestion of high amounts of aflatoxin. Today there is a mandate from the Food and Drug Administration limiting aflatoxin levels to 20 ppb in food products and 0.5 ppb in milk. Any food contamination with aflatoxin above these levels should not be used for human consumption. Many food processors have established vigorous screening programs for aflatoxin in their raw materials.

Aflatoxin is present in the spores of A. flavus, which can be produced in great abundance on the ears of fungus-infected corn. When the corn is combined and unloaded at elevators or other transfer points, it can generate considerable dust, some of which may contain aflatoxin. Dust collected near a combine in Georgia contained between 2,030 and 41,200 ppb of aflatoxin. The aflatoxin content of the dust collected at the elevator receiving this corn ranged from 621 to 1,480 ppb. Dust masks should always be worn when handling obviously moldy corn or peanuts. Inhaling aflatoxin-contaminated dust is presumed to be a health hazard. “Farmer’s lung” is a disease that often 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 the dust. Pulmonary mycotoxicosis is a disease that occurs in farmers when they frequently inhale large amounts grain dust containing fungal spores. This latter disease is a direct effect of the fungal toxins, and not an allergic reaction.


[Top of Page]