Key points about aflatoxin poisoning
- Aflatoxin is a substance produced by two particular greenish-grey moulds growing on grain and nuts.
- Aflatoxin in feed can poison livestock if they consume enough of it. Lower concentrations can produce residues in milk and meat.
- Drought and associated high temperatures increase aflatoxin content of peanut by-products, maize and sorghum. Contamination increases rapidly if these are not kept dry in storage. Bakery waste has a high risk of aflatoxin contamination if not kept dry.
- Grass, silage and pasture hay do not contain aflatoxin. However, peanut hay from drought-affected crops can contain enough aflatoxin to produce residues in milk if it contains more than 1 peanut pod/kg. Therefore, you should limit the amount you feed to dairy cattle.
- When purchasing grain or mixed feed, request written assurance from suppliers that it 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 they consume enough. Aflatoxins 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. Aflatoxin residues are found in liver for up to two weeks after consumption. Up to 5 per cent of ingested aflatoxin is passed into the milk of lactating mammals, so you must control the aflatoxin content of dairy feed.
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
- 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 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-to-late droughts often present a high risk of aflatoxin in rainfed crops, which increases contamination of peanut by-products. Feeding crop residues to livestock is also more likely during droughts.
Pigs have been poisoned on several occasions by peanut by-products, such as screenings. Likewise, fatalities in calves due to aflatoxin in peanut hay have also occurred.
Aflatoxin content of peanut hay depends on the number of peanut pods present in the hay, as the leaf and stalk contain 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. Therefore, to meet the Queensland stockfood standard of 0.2 mg/kg for peanut by-products, the peanut content of hay might needs to be below 0.2 per cent 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 less than about 10 per cent of the total diet of dairy cows. If the hay is to be fed to mature beef cattle, 25 per cent in the total diet should be safe, but avoid feeding cattle within two weeks of slaughter.
Maize and sorghum
Aflatoxin contamination also occurs in maize and sorghum, particularly 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.
Aflatoxin can contaminate other crops, such as 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 can I minimise risks to livestock health, and residues in meat and milk
The risk to livestock health is generally quite low if grain and mixed feeds are stored in good conditions. The risk increases during droughts when the aflatoxin content of some crops increases and more crop by-products are fed. There is a slight risk of aflatoxin residues in offal of cattle that consume large amounts of grain. These persist 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 residues are not destroyed by milk pasteurisation, and will transfer into powdered milk, yoghurt and other milk-based products.
As milk contamination could have severe economic consequences for both the farmer and the industry as a whole, you should do the following:
- 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 written assurance from their supplier that it meets Queensland stockfood standards for aflatoxin.