Nutritionist > Equine

Aflatoxin
Aflatoxins are of concern in warm and humid climatic conditions. Aflatoxins may be produced by certain Aspergillus species of fungi at environmental temperatures greater than 70 degrees Fahrenheit and at moisture levels greater than 14%. Although aflatoxins are not considered to be a major problem in cold or more temperate regions, care should be taken in colder climates when using feedstuffs such as maize, soya beans, oilseeds and other cereal grains, imported from warm and humid countries.

Aflatoxins are difuranocoumarin derivatives produced by many strains of Aspergillus parasiticus and Aspergillus flavus. Aflatoxins are found in feedstuffs such as maize on the field and also when stored. Crops may become contaminated with aflatoxin on the field when environmental conditions are right

The feeding of corn on a farm in Arkansas resulted in the death of three horses and many others suffered health problems. Investigations showed severe hepatic necrosis suggesting involvement of aflatoxin. Further feed analyses showed the presence of numerous colonies of Aspergillus flavus and chemical analyses showed the presence of aflatoxin B1 B2 and M1.

In addition ponies fed diets containing 2ppm aflatoxin per day showed higher levels of liver enzymes including GGT (gamma glutamyl transferase) indicating liver damage. There are reports of much lower concentrations of 0.3 ppm causing death in horses.

In all species, aflatoxins are hepatotoxic and carcinogenic with fatty changes causing hepatocyte degeneration, necrosis, and altered liver function. Suppression of liver protein synthesis is the main factor resulting in growth suppression. Aflatoxin is also known to interfere with vitamin D metabolism, contributing to reduced bone strength. By reducing bile salt production, aflatoxin negatively affects lipid and pigment absorption. Additionally the metabolism of other minerals including iron, phosphorus and copper are also affected by aflatoxin.

The maximum aflatoxin levels suggested for mature horses should not exceed 50ppb and breeding stock and working horses should preferably be fed aflatoxin free diets. Other tolerance levels cited suggest 20ppb (0.02ppm) and so there is a wide range of levels associated with clinical symptoms.

Clinical signs of aflatoxin toxicity include:

• Loss of weight / loss of appetite
• Reduce feed conversion efficiency
• Immune suppression and increased disease susceptibility
• Reduced fertility
• Liver necrosis
• Death