The Invisible Poison in Your Feed
Mycotoxins — toxic compounds produced by fungi growing on feed and forage — are one of the most common yet overlooked poisoning risks in livestock production. Unlike visible mold, which cattle often avoid, mycotoxins can be present in feeds that look perfectly normal. These invisible toxins cost the livestock industry billions annually and can affect every system in the animal's body.
This guide covers the major mycotoxins, what promotes their growth, how to recognize contaminated feeds, symptoms in cattle, and practical prevention strategies.
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Understanding Mycotoxins
What Are Mycotoxins?
Mycotoxins are secondary metabolites produced by fungi (molds). Key characteristics:
- Not alive: Unlike mold itself, mycotoxins are chemical compounds
- Heat-stable: Survive feed processing, including pelleting and extrusion
- Persistent: Don't break down during storage
- Cumulative: Low-level exposure over time causes damage
- Synergistic: Multiple mycotoxins together cause greater harm
Why Cattle Are Vulnerable
While ruminants have some natural defenses against mycotoxins (rumen microbes can degrade some compounds), cattle remain vulnerable because:
- Some mycotoxins are rumen-stable
- High-producing animals have limited detoxification capacity
- Stressed animals are more susceptible
- Multiple mycotoxin exposure overwhelms defenses
- Young animals particularly sensitive
Major Mycotoxins in Cattle Feeds
Aflatoxins
- Cottonseed and cottonseed meal
- Peanuts and peanut products
- Sorghum grain
- Insect damage to kernels
- Hot, humid storage conditions
- Temperatures 77-95°F, humidity >85%
- Reduced milk production
- Immune suppression
- Reduced feed efficiency
- Reproductive problems
- Cancer risk (aflatoxin B1)
Fumonisins
- Sorghum
- Wheat
- Late harvest
- Insect damage
- Hot, humid weather during grain fill
- Liver and kidney damage at high levels
- Reduced weight gain
- Immune suppression
Deoxynivalenol (DON/Vomitoxin)
- Barley
- Corn
- Oats
- Fusarium head blight (scab) in small grains
- Delayed harvest in wet conditions
- Reduced weight gain
- Diarrhea
- Immune suppression
- Reproductive issues at high levels
Zearalenone
- Wheat
- Barley
- Moldy hay
- High moisture
- Extended storage time
- Field infection before harvest
- Reproductive problems
- Vulvar swelling in heifers
- Decreased conception rates
- Mammary development in heifers
- Can affect bulls (reduced libido, testicular effects)
Ergot Alkaloids
- Endophyte-infected tall fescue
- Some other grasses
- Infected tall fescue pastures
- Contaminated grain or screenings
- Vasoconstriction (reduced blood flow)
- Heat intolerance
- Gangrene of extremities (severe cases)
- Reduced milk production
- Poor weight gain
- Reproductive failure
Ochratoxin A
- Corn
- Coffee and cocoa (not typical cattle feeds)
- Wet harvest
- High-moisture storage
- Immune suppression
- Ruminants somewhat protected by rumen degradation
Conditions Promoting Mycotoxin Production
In the Field (Pre-Harvest)
| Condition | Risk Factor | Primary Mycotoxins |
|---|---|---|
| Drought stress | HIGH | Aflatoxin |
| Insect damage | HIGH | Aflatoxin, Fumonisin |
| Cool, wet flowering | MODERATE | DON, Zearalenone |
| Hail damage | MODERATE | Multiple |
| Early frost | MODERATE | Multiple |
| Delayed harvest | HIGH | DON, Fumonisin |
In Storage (Post-Harvest)
| Condition | Risk Factor | Primary Mycotoxins |
|---|---|---|
| Moisture >15% | HIGH | Most types |
| Temperature >70°F | HIGH | Aflatoxin |
| Poor aeration | MODERATE | Multiple |
| Broken kernels | MODERATE | Multiple |
| Foreign material | MODERATE | Multiple |
| Long storage time | MODERATE | Ochratoxin, Zearalenone |
In Hay and Silage
- Rain damage before baling
- Poor storage (ground contact, leaking cover)
- Extended storage in humid conditions
- Slow filling/sealing
- Air infiltration after sealing
- Face management allowing aerobic spoilage
Recognizing Contaminated Feeds
Visual Indicators
- Musty or off odors
- Discoloration of grain
- Caking or clumping
- Heating in stored grain
- Black/purple ergot bodies in grain
When to Test
- Silage at opening
- Any feed after suspicious storage conditions
- When animals show unexplained symptoms
- Multiple animals showing symptoms
- Production decline without other explanation
- Feed refusal
Testing Options
- Test for specific mycotoxins of concern
- Typical turnaround: 3-7 days
- Cost: $25-100 per sample per mycotoxin
- Results in minutes to hours
- Less precise than laboratory
- Good for screening decisions
- Minimum 2 pounds composite sample
- Store in clean, dry container
- Refrigerate until shipping
- Submit promptly
Clinical Signs in Cattle
General Signs (Multiple Mycotoxins)
- Reduced feed intake
- Poor weight gain
- Rough hair coat
- Decreased milk production
- Increased susceptibility to disease
- Poor reproductive performance
Specific Syndromes
- Liver enlargement
- Decreased milk production
- Off-flavor milk
- Blood abnormalities
- Excessive salivation
- Elevated body temperature
- Lameness
- Loss of tail switch, ear tips
- Reduced weight gain
- Rectal or vaginal prolapse
- Mammary development (pre-breeding heifers)
- Irregular estrus
- Early embryonic death
- Animals appear hungry but won't eat
- Recovery when clean feed provided
Differential Diagnosis
Mycotoxicosis signs overlap with many conditions. Consider mycotoxins when:
- Multiple animals affected simultaneously
- Recent feed change preceded symptoms
- Signs don't fit other diagnoses
- Treatment for other conditions fails
- Production issues without obvious cause
Prevention Strategies
Purchasing Decisions
- Request mycotoxin testing results
- Inspect before accepting delivery
- Reject obviously damaged or moldy grain
- Consider source region and harvest conditions
- Check interior of several bales
- Reject any with visible mold or off-odors
- Know storage history
- Buy from reliable sources
Storage Management
- Clean bins thoroughly before filling
- Remove fines and broken kernels
- Aerate to maintain cool, uniform conditions
- Monitor temperature and moisture regularly
- Use first-in, first-out rotation
- Elevate bales off ground
- Allow air circulation
- Feed oldest hay first
- Monitor for heating or moisture
- Achieve adequate compaction
- Use quality plastic and weight it well
- Maintain proper face management
- Remove spoiled material before feeding
Feeding Strategies
- Reduces overall mycotoxin concentration
- Must know actual contamination levels
- May still be problematic for sensitive animals
- Clays (bentonite) effective for aflatoxin
- Modified clays and yeast products for broader spectrum
- Not 100% effective—prevent exposure when possible
- High-value/sensitive animals get cleanest feed
- Discard severely contaminated lots
Mycotoxin Action Levels for Cattle
FDA Guidance and Industry Standards
| Mycotoxin | Dairy Cattle | Beef Cattle |
|---|---|---|
| Aflatoxin | 20 ppb | 300 ppb |
| DON | 5 ppm (40% of diet) | 10 ppm (40% of diet) |
| Fumonisin | 30 ppm (50% of diet) | 60 ppm (50% of diet) |
| Zearalenone | <0.5 ppm | <0.5 ppm (breeding) |
- Multiple mycotoxins require lower individual limits
- Stressed or young animals more sensitive
- When in doubt, don't feed
Milk Testing
- Failed tests mean rejected milk
- Economic and regulatory consequences
- Feed testing essential for prevention
Response to Suspected Mycotoxicosis
Immediate Actions
- Stop feeding suspect feed
- Collect samples from multiple locations in feed source
- Submit samples for laboratory testing
- Document symptoms in affected animals
- Call veterinarian for diagnosis support
- Provide clean feed immediately
Veterinary Support
- Blood chemistry panels
- Biopsy (liver, kidney in severe cases)
- Necropsy of deceased animals
- Tissue mycotoxin testing
- No specific antidotes for most mycotoxins
- Remove contaminated feed
- Support liver/kidney function as needed
- Time and clean nutrition for recovery
Economic Recovery
- Veterinary diagnosis and records
- Production loss data
- Receipts for contaminated feed
- Disposal costs
- Contact attorney if significant losses
- Warranty and fitness claims may apply
Regional Considerations for Texas
Common Risk Periods
- Drought stress increases contamination
- Silage harvest quality critical
- Delayed harvest increases DON
- Hay quality concerns with late rains
- Watch for heating in grain
- Hay supplies may be marginal quality
Fescue in Texas
- Endophyte-infected fescue causes problems
- Novel endophyte varieties available
- Test pastures if fescue present
Resources
Testing Laboratories
- Phone: (979) 845-3414
- IDEXX Laboratories
- Romer Labs
Educational Resources
- Texas A&M AgriLife Extension - Mycotoxin resources
- FDA Mycotoxin guidance documents
- Council for Agricultural Science and Technology
Emergency Contacts
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The Bottom Line on Mycotoxins
Mycotoxin contamination is an invisible threat that demands proactive management. Testing and prevention cost very little compared to the production losses, animal health costs, and regulatory headaches that contaminated feed can cause.
Key principles for mycotoxin management:
- Buy quality feeds from reputable sources
- Store properly to prevent mold growth
- Test when conditions or symptoms warrant
- Remove suspect feeds promptly
- Use binders as an additional layer of protection, not a substitute for quality
