In mid-September, a milk processor in the Midwest was forced to dump four loads of milk. Test results showed milk aflatoxin levels were too high. Several thousands of dollars in profit poured down the drain.

Luckily, swift action by farm management put the farm’s milk back on the market after 24 hours, preventing further economic loss.

According to the Food and Drug Administration, aflatoxin levels in milk for human consumption cannot exceed 0.5 parts per billion (ppb). This year’s unrelenting drought has made this mandate a real challenge for many farms. If you find yourself with contaminated feed, here are some steps that you can take to protect not only the health of your animals, but also the safety of your milk supply.

Know your risk

The foremost step you can take to protect your milk supply and consumer confidence is to monitor aflatoxin levels in milk.

“When you look at aflatoxin tests on your farm, the one that’s always right is the milk,” says Mike Hutjens, professor emeritus and extension dairy specialist at the University of Illinois.

Feed monitoring also is a must, although frustrating because results of sampled feeds often show only very low levels of aflatoxin are present.

Both corn grain and silage can harbor aflatoxin, but don’t forget to step up quality control of by-products and other purchased feedstuffs that originated in drought- or heat-stressed areas.

Some corn by-products can actually raise aflatoxin levels in the diet, Hutjens points out.

For example, the concentration of aflatoxin in corn distillers grains can be three times higher than the original level found in the corn grain used for ethanol production. So, if corn grain contains 10 ppb aflatoxin, the level in the distillers grains could end up being 30 ppb, which exceeds the FDA’s 20 ppb limit for lactating dairy cows.

Corn gluten feed, corn hominy and fuzzy cottonseed are some other common by-product feeds that can harbor aflatoxin, so know what you are dealing with when using these feeds.

Unfortunately, it can be challenging to sample stored feed for aflatoxin contamination. Detailed instructions for proper sampling can be found at

Once there, type “Aflatoxin sampling instructions” into the “Search” box on the homepage.

Feeding options

Since no more than 20 ppb of aflatoxin are allowed in lactating-cow diets, you need to take action if you find yourself with contaminated feeds. Here are some options for managing the ration:

Dilute contaminated feed. This can be accomplished with “wholesome” forages and grains, such as alfalfa, barley, or commercial protein supplements and by-products like soy hulls, Hutjens says.

Use an additive or flow agent. There are three general types of flow agents (also known as mycotoxin binders). These include clay-based products, such as those containing bentonite, zeolite or calcium aluminosilicate, as well as products containing yeast cell wall extracts (also known as MOS agents or glucomannans) and those containing enzymes specific to mycotoxin control. Ask your nutritionist to help you determine what commercial product is a good fit for your situation and be sure to follow the manufacturer’s guidelines for dietary inclusion levels.

Ammoniate the corn. The process of ammoniation breaks or destroys the structure of the aflatoxin. Ideally, you need to have moisture (>13 percent) and heat (60° F) to cause this chemical reaction, Hutjens says. To accomplish this, seal the contaminated feed in bags or bins and then add ammonia. The level of ammonia to add will vary, depending on the concentration of aflatoxin in the feed. Be aware that the corn will darken because the sugars caramelize during ammoniation. You also may encounter palatability problems, so plan to aerate the feed. And as a safety reminder, be very careful when handling anhydrous ammonia.

Dry the corn. If you have corn yet to harvest, don’t store atrisk wet corn as high-moisture corn this year. “It’s a wonderful environment to grow the aflatoxin,” Hutjens says. “Dry it down below 14 percent moisture.”

A dairy cow secretes about 1 to 2 percent of the aflatoxin she consumes into her milk. Monitor and manage to keep your rations clean and your milk supply wholesome and safe.