Gibberella Ear Rot Signals Mycotoxin Risk in 2026 Corn Silage, Ohio State Specialist Warns

Dairy producers harvesting corn silage in 2026 should be alert to mycotoxin risks after reports of Gibberella ear rot emerged across Ohio, according to Jason Hartschuh, an assistant professor and field specialist in dairy management and precision livestock at Ohio State University Extension.

Writing in Farm and Dairy on 23 September 2026, Hartschuh said that visual signs of Gibberella ear rot during harvest are an early indicator that both Deoxynivalenol (DON) and Zearalenone (ZEA) may be present in this season's corn silage. He cautioned, however, that field observations alone cannot quantify contamination levels, and recommended that producers test silage now and again at feed-out.

DON Behaviour During Fermentation

Hartschuh explained that DON levels are not static during the ensiling process. According to his column, "DON levels stabilize after fermentation, levels can change during the first 60 days of fermentation, especially during the first 30 days." He noted that the toxin can shift between forms: the plant initially detoxifies DON by producing Deoxynivalenol 3-glucoside (D3G), a masked form, but fermentation or digestion can reverse this process, returning the compound to its more toxic state. Good silage management — specifically oxygen exclusion and high packing densities — can help limit DON increases during that window, he wrote.

Regulatory Thresholds Vary by Country

The column highlighted significant international variation in permitted DON levels for lactating dairy cows. Hartschuh noted that "Canada regulating DON levels for lactating dairy cows at 1 ppm while the U.S. recommends diets be below 5 ppm and Europe recommending less than 5 ppm." He also cautioned that mycotoxins rarely occur in isolation, complicating the application of single-toxin thresholds.

Rumen Environment Affects Detoxification

Rumen pH plays a key role in how effectively cattle can neutralise DON, Hartschuh wrote. He explained that DON can be converted in the rumen to Deep-deoxynivalenol (DOM-1), "a derivative of DON that exhibits less toxicity to the intestinal barrier function," but that the efficiency of this conversion depends on diet and rumen conditions. In dry cows at low rumen pH (5.8), "the low pH only reduced DON levels by about 30% while at a 6.8 pH most of the DON was converted in DOM-1 in 24 hours," he stated. ZEA behaviour differed: "ZEA has minimal form change in a 6.8 pH rumen environment while levels increased under acidosis with a rumen pH of 5.8."

Health Effects on Dairy Cows

Hartschuh outlined a broad range of potential adverse effects from DON exposure in dairy cows. While he noted that "DON often does not reduce milk production pounds, it can have many other adverse effects, including reducing milk protein levels," at the cellular level DON can inhibit protein synthesis, trigger a ribotoxic stress response activating proinflammatory cytokines, cause oxidative stress in multiple organs, and damage gut integrity. Long-term exposure, he noted, has in some studies been associated with "damage and reduced size in rumen epithelial cells."

For reproductive performance, Hartschuh identified ZEA as the larger concern. He described it as "an estrogen-mimicking toxin" that "binds to estrogen receptors, interfering with animals' reproductive function." Unlike DON, which the rumen partially detoxifies, ZEA metabolism produces one metabolite that is "60 times more potent, while the other is 0.2 times as potent." He cited research finding that diet levels as low as 0.3 mg/kg lowered oocyte quality in heifers, and that other studies found inflammation in the reproductive tract and lower oocyte maturation.

Management and Mitigation

Hartschuh noted that common mycotoxin binders have limited effectiveness against both toxins: "organoclays do not bind well to DON or ZEA." He indicated that organic clay combined with green seaweed cell wall material may reduce ZEA exposure when used together, while DON management is "best managed through products that improve gut health and encourage the biotransformation to the less toxic metabolite DOM-1." He added that antioxidants and feeding strategies that reduce inflammation and support immune function "can benefit high-DON diets," though he cautioned that rumen pH and passage rate affect the efficacy of most products.