Field reports of aflatoxin contamination of corn and corn silage are coming in, particularly from southern states where wet growing and harvest conditions were common this season. Some processors have also had to dump tankers of milk because contamination levels exceeded safe level of 0.5 parts per billion.
Other mycotoxins are also a concern this year, and proper bunker management is critical to prevent contaminated feed, says Lon Whitlow, a mycotoxin expert with North Carolina State University. "Approximately 1.7% of consumed aflatoxin in feed is transferred to the milk," he says.
Acute mycotoxin toxicity is usually not a problem because the cow’s rumen will destroy a large proportion of many mycotoxins, Whitlow says. But chronic problems, more difficult to diagnose, can persist. Chronic levels can lead to reduced feed intake, altered rumen fermentation and digestive upset, diarrhea, intestinal irritation, lethargy, reduced milk production and lowered reproductive rates. Mycotoxins can also suppress immunity, making cattle more vulnerable to disease, says Whitlow. Vaccines also might be less effective in the presence of mycotoxins.
"Robust rumen fermentation is important in mycotoxin prevention by maximizing mycotoxin degradation in the rumen," says Whitlow. "The use of buffers, sufficient effective fiber and microbials to stimulate rumen function can be helpful."
If mycotoxin contamination is suspected, the use of absorbents to prevent animal absorption and antioxidants to reduce oxidative stress also might be prudent.
To prevent mycotoxin growth in silage, air must be excluded from the silage pack. That means corn should be harvested at the proper moisture for dense packing. The use of an inoculant to enhance fermentation and sealing the silo immediately after filling are also critical.
After opening the silage, 6" to 12" of the silage face should be removed daily. The use of a facer is also highly recommended to ensure a clean, air-tight feeding face. Any spoiled or moldy silage should be discarded.
Whitlow’s presentation Wednesday, held in conjunction with World Dairy Expo, was sponsored by Prince Agri Products. See excerpts from his presentation here.