Avoid aflatoxin poisoning of livestock and the potential for residues in milk and meat

Key points

• Aflatoxin is a substance produced by two particular greenish-grey moulds growing on grain and nuts.
• Aflatoxin in feed can poison livestock if enough is consumed. Lower concentrations can produce residues in milk and meat.
• Drought and associated high temperatures increases aflatoxin content of peanut by-products, maize and sorghum, and contamination increases rapidly if these are not kept dry in storage. Bakery waste has a high risk of aflatoxin contamination if this is not kept dry.
• Grass, silage and pasture hay do not contain aflatoxin. However, peanut hay from drought-affected crops can contain sufficient aflatoxin to produce residues in milk, if it contains >1 peanut pod/kg, so limit the amount fed to dairy cattle.
• When purchasing grain or mixed feed, seek a written assurance from suppliers that the material meets regulated standards for aflatoxin.

What are aflatoxins?

Aflatoxins are substances produced by the greenish-grey moulds Aspergillus flavus and Aspergillus parasiticus in crops, particularly peanuts and maize. Livestock can be poisoned if enough is consumed, and they can also cause human liver cancer. Consequently, aflatoxins are regulated in feed and foods worldwide. The main aflatoxin found in crops is called aflatoxin B1, which is converted to aflatoxin M1 in the liver of mammals. Residues can remain in liver for up to 2 weeks after aflatoxin consumption. Up to 5% of ingested aflatoxin is passed into the milk of lactating mammals, so the aflatoxin content of dairy feed must be controlled.

What standards apply to aflatoxin in stockfoods in Queensland?

The Agricultural Standards Act 1994 and the Agricultural Standards Regulation 1997 set Queensland stock food standards that limit contamination to: 0.2 mg aflatoxin B1/kg in peanut by-products; 0.02 mg aflatoxin B1/kg in grain; 0.05 mg/kg in stock food for beef cattle, horses and sheep, 0.02 mg aflatoxin B1/kg in stock food for dairy cattle; and various levels in stock foods for other classes of stock.

What feeds are contaminated in Queensland and why?

Aflatoxin contamination is a serious problem in peanuts grown in the Burnett region. The peanut industry minimises aflatoxin content of nuts destined for human food through advanced growing, harvesting and drying practices, price penalties and stringent grading. Contamination increases during drought when the plant defences are weakened by moisture stress. Aflatoxin minimisation in peanut production reduces contamination in by-products like peanut hay, but this might not apply to failed peanut crops that are baled for hay.  Peanut hay derived from irrigated production has less aflatoxin. Seasons with mid-late droughts such as 2004-05 present a high risk of aflatoxin in rainfed crops, which increases contamination of peanut by-products. Feeding crop residues to livestock also increases during droughts.

Pigs have been poisoned on several occasions by peanut by-products such as screenings. Fatalities in calves due to aflatoxin in peanut hay from the Burnett region have also occurred. Aflatoxin content of peanut hay depends on the amount of peanut pods present in the hay, as the leaf and stalk material contains little toxin. Adult cattle are less likely to be poisoned than calves, but can have residues in milk and offal. Peanuts from drought-stressed crops can contain >100 mg/kg of aflatoxin, so to meet the Queensland stockfood standard of 0.2 mg/kg for peanut by-products, the peanut content of hay might need to be below 0.2% by weight (< 1 pod per kg of hay). To minimise the risk of residues in milk, peanut meals, and peanut hay containing pods should comprise no more than about 10% of the total diet of dairy cows. If the hay is to be fed to mature beef cattle, 25% in the total diet should be safe, but avoid feeding cattle within two weeks of slaughter.

Aflatoxin contamination also occurs in maize and sorghum, and this rises in drought conditions. The concentrations present at harvest are usually not enough to poison livestock, but can rapidly escalate in hot spots in storage if the grain is moist or not aerated properly. Pigs have been poisoned on several occasions from mouldy maize and sorghum. A current project Managing mycotoxins in maize supported by DPI&F, the Grains Research and Development Corporation and the maize industry, is seeking to improve our ability to predict aflatoxin contamination and deal with it when it occurs. Aflatoxin can contaminate other crops like wheat, barley and oilseeds if these become mouldy in storage, but to a much lesser extent than peanuts and maize. Bread (bakery waste) can also develop very high aflatoxin concentrations if it becomes moist, and this has poisoned pigs and dogs on several occasions.

How to minimise risks to livestock health, and residues in meat and milk

The risk to livestock health is generally quite low, providing that grain and mixed feeds are stored in good conditions. The risk does increase during droughts, when aflatoxin content of some crops increases, and also more crop by-products are fed. There is a slight risk of aflatoxin residues in meat of cattle consuming large amounts of grain, but confined to the offal, and persisting for 1-2 weeks after exposure.

The dairy industry conducts aflatoxin testing of milk as part of the Australian Milk Residue Analysis (AMRA) survey.  The sensitivity of tests for residues is increasing rapidly, as is the concern of consumers about food safety and residues in general. Aflatoxin M1 is not destroyed by pasteurisation of milk, and will transfer into powdered milk, yoghurt and other milk-based products.  Contamination of milk could have severe economic consequences for the particular farmer and the industry as a whole. Limit the use of peanut meals and by-product in dairies. Ensure feed grain is stored in conditions that avoid mould growth. Harvest grain at recommended moisture content, dry if necessary and maintain good aeration and insect control. Regularly clean feed bins. Take particular care with bakery wastes.

Pasture-based beef, sheep and dairy production systems present low risk because aflatoxins are not produced in pasture, grass hays and silage - the aflatoxin risk is largely confined to feeding of grain-based concentrates, peanut by-product, bakery waste and possibly material containing fruit and vegetable by-products. Livestock producers and dairies purchasing grain and mixed feed should obtain a written assurance from their supplier that it meets Queensland stockfood standards for aflatoxin.