Mycotoxins: The Unseen Adulterator

What are mycotoxins?

Mycotoxins are toxic compounds produced by molds that commonly grow on corn, small grains, cottonseed, byproducts and forages used in dairy rations. They are chemically diverse, heat-stable, and often present even when visible mold is minimal or absent, which makes them an “unseen” threat in the total mixed ration (TMR).

The most relevant mycotoxins in TMR include aflatoxins, deoxynivalenol (DON, vomitoxin), zearalenone, fumonisins, ochratoxin A and T-2 toxins. Different fungi species thrive under different weather and storage conditions, so yearly toxin profiles can shift with growing season stress and on-farm storage practices.

 

Why is TMR a high‑risk vector?

TMR brings together silage, dry forages, grains and byproducts, so any contaminated ingredient adds to the overall mycotoxin load in the bunk. Studies reviewing TMR contamination show that “double” and “multiple” mycotoxin co-contamination are the rule rather than the exception, even when individual levels appear low.

Because feed is finely chopped and mixed, cows cannot selectively avoid problem ingredients, and consistent exposure occurs in every bite. High-producing cows consume greater dry matter, which increases daily mycotoxin intake and can overwhelm natural rumen detoxification.

 

How do mycotoxins act in the cow?

Rumen microbes can partially degrade some mycotoxins, but this capacity is limited and depends on rumen pH, passage rate and toxin type. High-intake, high-concentrate diets speed passage rate and can reduce ruminal detoxification time, making high-producing cows more sensitive to typical field levels.

Mycotoxins that bypass the rumen are absorbed in the intestine and must be detoxified by the liver and kidneys, contributing to oxidative stress and systemic inflammation. Experimental work has shown altered antioxidant capacity, changes in metabolites linked to amino acid metabolism, and shifts in rumen fermentation when cows receive contaminated diets.

 

The “unseen adulterator” of performance

Even at so‑called “typical” contamination levels, mycotoxins depress feed efficiency and nutrient digestibility. In controlled trials where cows received diets contaminated with DON and fumonisins at levels commonly seen on commercial dairies, researchers reported lower total-tract dry matter and fiber digestibility and a drop of about 1 to 1.5 kilograms of milk per day.

Beyond milk yield, field and research reports link mycotoxins with reduced dry matter intake, poorer body condition, and decreased reproductive performance. These effects rarely appear as a single dramatic event; instead, they accumulate as lost milk, more days open, and higher cull rates – the “unseen cost” inside the TMR.

 

Health, immunity and udder

Mycotoxins compromise gut integrity and immune competence, increasing susceptibility to disease. Review and trial data associate contaminated rations with higher incidence of mastitis, elevated somatic cell count (SCC), and greater risk of secondary infections.

In a long-term study where cows consumed naturally contaminated TMR, adding a mycotoxin-management feed additive was associated with improved blood immune markers and a reduction in SCC of more than 50% over two months, indicating better udder health. Reproductive challenges, such as lower conception rates and more early embryo loss, have also been described, particularly with estrogenic toxins like zearalenone.

 

Watch signs

Because symptoms are non-specific, mycotoxicosis often masquerades as “just a tough year” for cow health and performance. Common patterns dairy producers and nutritionists should watch for include:

·       Unexplained drops in milk yield and components despite adequate energy and protein.

·       Inconsistent intakes, feed refusal, sorting, or off-feed events not tied to ration changes.

·       Higher-than-expected SCC and mastitis, plus more treatments.

·       Fertility problems, irregular heats, early embryonic loss, and more repeat breeders.

·       Increased digestive upsets, diarrhea, or displaced abomasum without clear dietary causes.

 

Mycotoxin	Main sources in TMR	Primary issues in dairy cows	Notes on carryover or risk
Aflatoxins	Corn, cottonseed, improperly stored feeds	Liver damage, reduced performance; aflatoxin M1 in milk	Direct food-safety concern via milk residues
DON (vomitoxin)	Corn, small grains, corn silage	Lower intake, impaired rumen fermentation, milk drop	Often co-occurs with zearalenone and fumonisins
Zearalenone	Corn, small grains, some byproducts	Reproductive disorders from estrogenic activity	Can affect heifers and breeding stock at lower levels
Fumonisins	Corn and corn byproducts	Reduced digestibility, performance, possible immune impact	Frequently present with DON in TMR
Ochratoxin A	Cereal grains, stored feeds	Kidney damage, reduced performance, immune effects	Rumen can detoxify some, but not all, exposure

 

Testing and monitoring strategies

Modern surveillance emphasizes testing the complete TMR in addition to individual ingredients, as mixing tends to increase the chance of multiple co-occurring toxins. Reviewing recent TMR-focused research, authors highlight that TMR sampling gives a more realistic picture of what cows ingest and helps identify animals at risk via estimated daily intake calculations.

Regular sampling should target higher-risk ingredients (corn silage, high-moisture corn, small grains, cottonseed, and byproducts), as well as finished TMR when herd-level problems appear. Producers and nutritionists can work with laboratories that offer multi-mycotoxin panels, including “emerging” toxins that traditional screens may miss.

 

On-farm mitigation

Effective mycotoxin management starts in the field with hybrid selection, timely harvest and minimizing plant stress. Then continues through storage with good packing density, oxygen exclusion and face management on silage. Reducing spoilage yeasts and molds at the bunker face and avoiding re-heating in the TMR can limit additional toxin formation.

When risk is identified or suspected, feeding strategies often combine:

·       Ration reformulation to dilute high-risk ingredients and avoid highly contaminated lots.

·       Use of proven mycotoxin management products that bind, transform, or support metabolism of a broad spectrum of toxins.

·       Supportive nutrition (adequate antioxidants, trace minerals and vitamins) to help cows cope with oxidative stress and immune challenges.

 

Additives and Binders

Peer-reviewed and field studies report that well-designed mycotoxin management additives can improve immune parameters, lower SCC and help stabilize production in herds consuming contaminated TMR. These products may combine binders (such as specific clays or yeast cell wall components) with enzymatic or microbial agents and gut-support nutrients to address a wider spectrum of toxins.

In one trial with naturally contaminated TMR, cows receiving a mycotoxin management additive showed improved udder health and better blood indicators of immune function compared with cows on the same TMR without the additive, and benefits increased once the whole herd was supplemented. Such data aligns with the concept that mycotoxin control should be integrated into an overall herd health and nutrition program rather than treated as a one-time fix.

Effective combat

The real dilemma lies in choosing the right product or combination of products to combat mycotoxins.

1.    Feed Yeast to combat reduced intakes or feed refusals.

2.    Enzymes and probiotics improve nutrient absorption and repair disrupted metabolism caused by mycotoxins.

3.    Supportive nutrition supplies the immune system with what it needs bring altered endocrine and exocrine systems back into homeostasis.

4.    Immune modulators correct suppressed immune function and inflammation.

5.    Phytogenics fix altered liver function.

Intercept FEND provides comprehensive coverage when it comes to defending against “unseen adulterators” like mycotoxins.

 

Bringing it all together

For dairy operations, mycotoxins represent a chronic, often underestimated drag on performance that quietly reduces milk, fertility and herd health over time. Treating them as an “unseen adulterator” encourages routine monitoring, proactive ingredient management and strategic use of mitigation tools rather than reactive troubleshooting after problems are entrenched.

By combining regular TMR testing, strong forage and feed management, and evidence-based mycotoxin solutions, producers can protect cows’ rumen function, immunity and productivity while safeguarding milk quality and farm profitability.

 

Sources:

1.      https://pmc.ncbi.nlm.nih.gov/articles/PMC10867658/               

2.      https://www.agproud.com/articles/62075-mycotoxins-the-invisible-tax-inside-your-tmr          

3.      https://www.mcness.com/articles/mycotoxins-the-invisible-handicap/              

4.      https://pmc.ncbi.nlm.nih.gov/articles/PMC11598721/                   

5.      https://pubmed.ncbi.nlm.nih.gov/32252249/                 

6.      https://www.dsm-firmenich.com/anh/news/feed-talks/articles/typical-levels-of-mycotoxin-contamination-impact-the-performance-of-high-producing-dairy-cows.html            

7.      https://peerj.com/articles/8742/ 

8.      https://www.scielo.br/j/abmvz/a/4TsJPcRhyXdXjKZLGfKNhcN/       

9.      https://www.agproud.com/articles/61459-mitigating-mycotoxins-the-three-legged-milking-stool-approach

10. https://www.agproud.com/topics/462-feed-evaluation

Written by: Mariah Gull, M.S.