Understanding Aflatoxin Downgrades

Summary:

Here you’ll find what aflatoxin is, why it matters in milk, and how to manage the risks from contaminated feed.


Aflatoxin and other mycotoxins are heat-stable toxins produced by fungi. They are naturally occurring, found mostly in grain, but occasionally in hay and silage.

Downgrade support

Your milk quality results are available daily on your tanker docket or on the Farm Source website.

Aflatoxin residues in milk pose a high risk to human health due to their carcinogenic properties. Raw milk containing a level of ≥0.05 ppb (“parts per billion”) (50 ppt (“parts per trillion”) aflatoxin residue is deemed to be unacceptable, so therefore that milk cannot be used for manufacturing.

Testing for Aflatoxins in milk and feed

MilkTestNZ is able to test for the presence of aflatoxin residues in milk.

If aflatoxin levels in your milk exceed 20ppt, we may require testing of your milk before you can supply again. QCONZ are able to complete a traceback to assess current feed types on farm and take samples if required.

HortResearch and Hill Laboratories are able to test for aflatoxins in feed and milk.

If you cannot determine the cause of the test result or you receive downgrades, call the Farm Source Service Centre.

Depending on the duration and severity of the issue, they will organise an on-farm trace back and take you through the Milk Quality Support Programme.

A snapshot of causes:

  • Imported feeds like copra, corn silage, molasses and almond husks are higher risk for aflatoxin contamination.
  • Feed from hot, humid climates has a greater likelihood of aflatoxin developing.
  • Mould presence does not always mean aflatoxin, but risk increases under heat and humidity stress.
  • Crop damage from insects, weather or handling before harvest increases aflatoxin risk.
  • Delayed drying after harvest can lead to contamination and aflatoxin formation.
  • Warm, humid storage conditions promote aflatoxin, so keeping feed cool and dry is critical.
  • Aflatoxin can form before feed reaches the farm and cannot be removed once present.

What is aflatoxin?

Aflatoxins are toxins produced by certain fungi (moulds).
  • They are heat-stable, so they are not destroyed by processing.
  • When cows eat contaminated feed, aflatoxin is converted in the liver to aflatoxin M1.
  • Aflatoxin M1 can pass into milk and urine.

Why aflatoxin in milk is a problem

Even very small amounts of aflatoxin in milk are a serious food safety risk.
  • Aflatoxins are highly toxic and carcinogenic to animals and humans.
  • Milk with aflatoxin residues above the limit cannot be used for manufacturing.
  • Pasteurisation does not destroy aflatoxin M1, so it can carry through into dairy products.

Maximum residue levels for milk and feed

  • Bulk milk tank limit: 0.05 ppb (50 ppt) aflatoxin residue.
  • Infant formula products: 25 ppt.
  • Maximum allowable level in dairy cow feed: 5 ppb.

What causes aflatoxin production

  • Produced by moulds that grow in warm, dry conditions.
  • Mould presence does not always mean aflatoxin is present.
  • Aflatoxin develops when moulds are stressed by high heat and humidity.
  • Contamination can occur before harvest, after harvest, or during storage.

Feeds that are higher risk in New Zealand

  • Imported feeds are the main risk.
  • Examples include copra, imported corn silage, molasses, and almond husks.
  • Feeds from warm, humid climates carry a higher risk.

 

How can farmers control risk

Once aflatoxin is produced, it cannot be eliminated.

  • Prevent fungal growth where possible at every stage.
  • Pre-harvest risks include insect damage, mechanical damage, drought stress, and heavy rainfall.
  • Post-harvest risk increases if crop drying is delayed.
  • Storage is the main stage farmers can control.
  • Store feed in cool, dry conditions.

  • MilkTestNZ can test milk for aflatoxin residues.
  • If milk exceeds 20 ppt, testing may be required before you can supply again.
  • QCONZ can help with feed traceback and on-farm sampling.
  • HortResearch and Hill Laboratories can test feed and milk for aflatoxins.
  • Source feed from reputable suppliers and ensure it has been tested below 5 ppb.
  • Follow storage and feeding instructions and don’t use feed past its expiry date.
  • Keep feed cool and dry.
  • Avoid feeding mouldy feed.
  • Keep clear records of feed types and how they are fed for traceability.
  • Copra is a higher-risk feed and should not exceed 15% of the total diet.

Get support

  • Concerned about aflatoxin in your milk? Contact MilkTestNZ to arrange testing and understand your results.
  • Unsure which feed could be the source? Work with QCONZ to trace feeds on farm and arrange sampling if needed.
  • Want to check feed before feeding it out? Talk to an approved laboratory about aflatoxin testing for feed.