Preventing mycotoxin contamination in corn silage requires a multi-pronged approach, including field management, proper harvesting, ensiling techniques, and strategic feeding practices. Regular testing and proactive adjustments can help maintain silage quality and safeguard animal health and performance. By following these guidelines, farmers can minimize the risks posed by mycotoxins and ensure a healthier, more productive livestock feed supply.
What Are Mycotoxins?
Mycotoxins are toxic substances produced by certain fungi. These compounds are considered secondary metabolites, meaning they are not essential for fungal growth but are produced in response to stress or competition. Thousands of mycotoxins have been identified, and when consumed by animals, they can cause a condition called mycotoxicosis. Symptoms vary based on the specific toxin and the affected animal.
Mycotoxins can form both in the field and during storage. Environmental conditions and plant damage contribute to their presence. Additionally, multiple mycotoxins can interact negatively, compounding their harmful effects on animal health and performance.
Where Does Deoxynivalenol (DON) Come From?
Deoxynivalenol (DON), also known as vomitoxin, is produced by the fungus Fusarium graminearum (also called Gibberella zeae), which causes Gibberella ear rot and crown and stalk rot in corn. The Great Lakes region provides an ideal environment for this pathogen, leading to frequent occurrences of these diseases in Wisconsin silage corn.
DON can accumulate in both the stalk and ear of the plant at different times, making it difficult to detect solely by scouting for ear rot. This highlights the importance of comprehensive monitoring, as mycotoxin contamination poses significant health risks that nutrition management alone cannot fully address.
Managing Deoxynivalenol in the Field
Several factors influence the presence of DON in corn fields:
- Fungal Survival: The fungi that produce DON can persist on crop residue, making residue management a potential, but not foolproof, control method. Wind can also spread fungal spores, so eliminating all risk is impossible.
- Hybrid Selection: Some corn hybrids, such as brown mid-rib (BMR) varieties, tend to accumulate higher DON levels than conventional hybrids. Switching to non-BMR hybrids may help reduce risk.
- Plant Density and Spacing: Managing plant populations to lower field humidity and minimize competition for nutrients can improve overall plant health and reduce mycotoxin risk.
- Fungicide Application: While fungicides can help, their effectiveness in reducing DON in Wisconsin has been inconsistent. The best results occur when applied within 5–7 days of white silk (R1 growth stage).
- Mange Insect Damage: Using Bt hybrids or insecticides may help by reducing insect damage, especially on the ears, which can create and opening for Fusarium to colonize and produce DON.
- Foliar Disease Control: Diseases like tar spot can reduce silage quality and weaken stalks, leading to lodging and moisture imbalances. Early chopping may mitigate some risks by improving fermentation and reducing mycotoxin buildup during storage.
Deoxynivalenol in Stored Corn Silage
Research has shown that DON levels in silage can increase during the first 30 days of storage, likely due to:
- Residual Oxygen: The fungi that produce DON thrive in aerobic conditions. If silage isn’t packed properly, oxygen pockets may allow continued fungal activity.
- Masked Mycotoxins: DON-3-glucoside (D3G) is a conjugated form of DON that is not detected in routine tests. During early ensiling, D3G may be converted back to DON, increasing its concentration later on in storage.
To minimize DON buildup:
- Pack and seal silage tightly with oxygen-barrier plastic.
- Consider testing for both DON and its conjugates to get an accurate contamination assessment.
Managing Mycotoxins in the Bunker
Balancing foliar disease and mycotoxin management is key to producing high-quality silage. Here’s how farmers can reduce DON risk at harvest and storage:
- Prioritize Diseased Fields: Harvest fields with foliar disease or ear rot first.
- Monitor Moisture: Chop at the optimal moisture level to ensure proper fermentation.
- Enhance Packing and Sealing: When disease pressures are high, take extra time to eliminate oxygen pockets.
- Alternative Harvesting Methods: If corn is too dry for silage, consider harvesting for high-moisture grain or snaplage instead.
- Frequent Testing: Regularly test silage for DON and other contaminants to make informed feed management decisions.
Managing Mycotoxins at Feedout
Since mycotoxins persist in stored silage, continuous monitoring is essential. Farmers can take several steps to mitigate their impact:
- Blending Contaminated Silage: Mixing affected silage with cleaner feed can help reduce the overall mycotoxin load in the total mixed ration (TMR).
- Using Feed Additives: Mycotoxin binders, probiotics, yeast-based supplements, and immune-boosting products can help counteract mycotoxin effects on digestion and animal health.
- Preventing Spoilage: Limit silage exposure to oxygen:
- Remove silage face at feeding time rather than exposing the rest of the feed to oxygen in advance.
- Ensure silage faces remain even and compact.
- Use preservatives if silage is heating or spoiling.
- Monitor bunker and bag storage for holes or damage and seal them immediately.