With drought and heat-stressed corn [...], mycotoxin levels could be elevated leading to animal health risks. Corn grain may exhibit signs of fungi growth and kernel damage. Mycotoxins are toxic byproducts produced by fungi that infect feed crops due to insect damage or stressed plants. These fungi produce mycotoxins that can include aflatoxin, zearalenone, T-2 and DON (deoxynivalenol) that can impact dairy cattle performance for several reasons, including:

1. reduced feed intake or feed refusal (poor performance)

2. reduced nutrient absorption and impaired nutrient metabolism (poor growth)

3. shifted hormonal levels (reduced reproduction)

4. suppressed immune system (increased health and disease risk)

5. depressed rumen microbial fermentation (lowered digestion and feed efficiency)

Young and pregnant animals are at great risk at higher levels of mycotoxins. Monogastric animals (swine) are at greater risk compared to adult ruminant animals (steers and older dairy heifers). Dairy cattle consume forages that dilute down contaminated grain. The following levels should be used as guidelines to minimize animal risk and for action guidelines:

•Zearalenone: less than 0.3 ppm (parts per million) or 300 ppb (parts per billion)

•DON: less than 1.0 ppm

•T-2 Toxin: less than 0.1 ppm

•Aflatoxin: less than 20 ppb (for milk cows), over 100 ppb for non-lactating cows

Aflatoxin is a concern with lactating dairy cows because cows can transfer 1 to 2 percent of consumed aflatoxin to milk. The FDA has set a legal maximum of 0.5 ppb in milk as the highest level in milk that can be marketed. If the total ration dry matter (DM) is over 20 ppb, a risk of contaminated milk can occur (for example, 2 percent of aflatoxin transfer in milk of a feed containing 30 ppb could result in 0.6 ppb in milk). Milk processing cooperatives and companies monitor milk for aflatoxin which protects consumers and provides valuable early warning for dairy managers.

The level of aflatoxin that will cause health and reproductive problems is higher than 100 ppb. If milk contains aflatoxin, dairy managers should remove the damaged feed. Milk levels of aflatoxin will drop within 24 to 48 hours after the damaged feed is removed.

The FDA has established guidelines for acceptable maximum levels of aflatoxin in corn:

•300 ppb for finishing beef cattle

•200 ppb for finishing swine (greater than 100 pounds)

•100 ppb for breeding beef cattle, breeding swine and mature poultry

•20 ppb for other animal feeds

Corn grain is normally a highest- risk feed for mycotoxins, but haylage silage and corn silage can contain mycotoxins. Fuzzy cottonseed can be another source in lactating cow rations.

Commercial labs can test damaged feed for mycotoxin. Taking a representative sample is critical to ensure the results reflect the actual levels. The cost to test will vary. Some labs can provide a combination of several mycotoxin tests at a lower price.

Pelleting and extruding of the grain will not reduce the mycotoxin levels present in the feed (roasting can reduce surface mycotoxin levels). Heating, aeration and proper handling can reduce the formation of additional mycotoxins, if corn grain is high in moisture when harvested.

Monitoring grain bins to stop mold growth is critical. Treating with anhydrous ammonia can reduce levels of aflatoxin. Diluting contaminated feed with wholesome feed can reduce the level consumed. PD

References omitted due to space but are available upon request.

—From 2006 University of Illinois Dairy Days Proceedings

Mike Hutjens

Professor of Animal Sciences

Q. When is mycotoxin risk the highest? What can a producer do now to prepare for that high-risk season?

Mycotoxin risk increases once the corn crop is harvested. Mold levels can explode if the grain storage favors mold growth (moisture, nutrients and heat). Another critical time occurs during late winter and spring when corn bins heat up (no air or heat) and condensation can occur, encouraging mycotoxin growth.

Corn silage can also contain higher levels of mycotoxins depending on insect damage, plant stress, heat or moisture stress and poor silage fermentation characteristics.

Strategies to minimize mycotoxin risk include selecting corn varieties that maintain heathy corn plants, drying down corn grain immediately after harvest to safe storage levels, enhancing corn silage fermentation (plant processing, adequate moisture for fermentation and growing a high moisture corn and adding an inoculant) and considering a mycotoxin binder, if “at risk” levels of mycotoxins develop

Q. Why is corn grain at highest risk among feeds for mycotoxins?

Corn grain is a high risk feed due to seed damage in the field and grain is an excellent nutrient source for molds to grow and thrive.

To contact Mike, e-mail him at hutjensm@ad.uiuc.edu