What you can do if you have corn silage that’s contaminated with aflatoxin.
Corn silage tests on the 2013 crop have shown high levels of aflatoxin in some areas. While most of the country still has corn in the field, tests coming in from the Southwest are showing high or very high levels of aflatoxin. Some dairies feeding 2013 silage have had to dump milk.
Total aflatoxin in feeds and foods like corn grain, cottonseed and peanuts is restricted by the FDA to 20 ppb. Aflatoxin B1 is the most toxic form of aflatoxin in feed and food. It is converted to aflatoxin M1 (AFM1) in milk. This is a less toxic metabolite, but nonetheless, it is more strictly regulated than B1 because of the high volume of dairy products consumed by humans. The FDA limits AFM1 to 0.5 ppb in milk, ensuring the safety of dairy products. About 1-3% of aflatoxin in feed is transferred to milk. So if, for example, a TMR contains an ingredient that is 100 ppb and it is 20% of the TMR, the AFM1 in milk could potentially be between .2 and .6 ppb.
The risk for aflatoxin in feeds and foods is higher in warm, humid areas or in drought stricken areas. It can develop in the seed or during storage.
So what do you do if you have a bunch of corn silage contaminated with aflatoxin? Unfortunately, if the aflatoxin levels are very high, the options are few.
1. Minimize your risk from other sources – corn grain, cottonseed, peanut products.
2. Since there may be hot spots in a pit of corn silage, we really don’t know at any one time how much aflatoxin is in the silage we are feeding. Test both the corn silage and the TMR regularly if you think there is a risk of contamination. Send the feed to a certified lab and identify the feed, since labs may use different testing procedures for cereal grains, forages or TMRs.
3. Limit the amount of silage in the TMR to reduce the risk of transfer to milk.
4. Bentonite clay has been shown to bind aflatoxin from the gastrointestinal tract. Refined clay products such as Novasil and AB20 (called smectite or montmorillonite clays) are more effective. An inclusion rate of .5% of the dry matter has been shown to be effective, although higher levels may be required. Recent research has shown that trace mineral and vitamin depletion when feeding clays may not be an issue, as previously thought. However, higher vitamin E levels may be warranted as a precaution. Non-clay binders may be more wide-spectrum but are not as specific for aflatoxin.
5. Ammoniation has been used in Arizona as an approved method to detoxify cottonseed over 20 ppb for dairy cattle. This is also effective for corn silage, although more difficult to apply after it is ensiled.
6. It takes about 12-24 hours for aflatoxin in contaminated feed to appear in milk. It takes about 1-4 days for milk to clear after the feed has been removed or an effective binder is fed.