When mycotoxin exposure is suspected, the feed sample is usually the place to start. Testing can identify which toxins are present and at what concentrations. Yet a feed analysis cannot necessarily tell you how much toxin an individual cow actually consumed or absorbed.
That is where mycotoxin biomarkers could offer another piece of the puzzle.
Researchers are investigating whether measurements in blood, urine and other biological samples can provide evidence of an animal’s internal exposure. The approach is still developing, and important questions remain about how biomarkers should be interpreted. However, recent research in cattle is demonstrating why looking beyond the feed sample could eventually give veterinarians another way to investigate suspected exposure.
DON and ZEN Biomarkers Offer a Look Inside the Cow
Dänike and colleagues evaluated deoxynivalenol (DON) and zearalenone (ZEN) residues in blood and urine from 244 dairy cows on 12 farms in Germany. The researchers used measurements of the toxins and their metabolites to estimate the cows’ dietary exposure.
The study addresses one of the limitations of conventional feed testing. Under practical feeding conditions, individual dry matter intake and body weight may be unknown, while mycotoxin concentrations can vary among feed ingredients, batches and the final mixed ration. A concentration measured in a feed sample therefore describes what was present in that sample, but may not accurately reflect an individual cow’s actual exposure.
Instead, the researchers looked at what was happening inside the animals.
By measuring mycotoxin residues and metabolites in blood and urine, they could use those measurements to work backward and estimate dietary exposure. These body fluid measurements estimated dietary DON concentrations at 0 to 1.6 mg/kg and ZEN concentrations at 0 to 3.0 mg/kg. Critical dietary concentrations for DON and ZEN are 5.0 and 0.5 mg/kg, respectively.
The results demonstrate the potential of biomarkers to provide information about exposure that a single feed sample cannot necessarily capture. At the same time, the study did not establish that differences in estimated mycotoxin exposure were causing differences in cow health or performance. Researchers found no relationship between estimated exposure and measured performance, reproductive or health traits.
More frequent, longitudinal measurements would be needed to better evaluate those relationships.
The biomarkers provided evidence of exposure, not a diagnosis of mycotoxicosis.
Metabolites May Provide Stronger Evidence Than the Parent Toxin
The DON results also illustrate why biomarker research is not simply about looking for the same toxin in a different sample.
In blood, de-epoxy-DON, a metabolite of DON, was detected in 82.4% of the 244 cows, while parent DON was detected in only 12.2%. In urine, de-epoxy-DON was detected in 95.7% of samples, compared with 53.7% for DON itself. The researchers therefore calculated total DON residues using DON, de-epoxy-DON and conjugated forms rather than relying solely on the parent compound.
That distinction is important when interpreting biological samples. Once a mycotoxin enters the animal, it does not simply remain unchanged. It can be metabolized, transformed into other compounds and eliminated through different routes.
A biomarker strategy therefore has to account for what happens to the toxin after exposure, not simply whether the original compound can be detected.
Aflatoxin Research Takes a Different Biomarker Approach
Ponnusamy and colleagues examined another way of looking for mycotoxin exposure. They evaluated serum aflatoxin B1 (AFB1)-albumin adducts and blood AFB1-DNA adducts as potential biomarkers of chronic exposure in 53 cattle from farms, a veterinary hospital and a slaughterhouse in India.
An adduct forms when a reactive compound binds to another molecule. After AFB1 is metabolized, it produces a highly reactive compound that can bind to proteins and DNA, creating AFB1-albumin and AFB1-DNA adducts.
The researchers detected both types of adducts across three different cattle groups.
They also tested feed from the farm and clinical cases. AFB1 was detected in 50% of the 40 feed samples available, with 70% of positive samples exceeding the study’s cited maximum permissible level.
Yet there was no significant correlation between feed contamination and biomarker concentrations.
That finding illustrates one reason researchers are interested in measuring the animal itself. A feed sample can establish that contamination was present in the material collected at a particular time and place. A biomarker can provide evidence that the animal was actually exposed and, depending on the biomarker, may provide information about exposure over a longer period.
The researchers identified AFB1-albumin as particularly useful for assessing chronic exposure because of its relatively longer biological half-life compared with some other aflatoxin biomarkers. They also suggested that combining albumin and DNA adduct measurements could help distinguish different aspects of exposure.
Different Biomarkers Answer Different Questions
There is unlikely to be one universal “mycotoxin biomarker.”
Researchers are investigating several types of evidence, each of which can provide different information about exposure:
- Parent mycotoxins in blood or urine can provide evidence that a toxin is present in the animal.
- Mycotoxin metabolites, such as de-epoxy-DON, can provide evidence of how the animal has processed the toxin and may be more readily detected than the parent compound.
- Protein adducts, such as AFB1-albumin, can provide evidence of exposure over a longer period.
- DNA adducts, such as AFB1-DNA, indicate that a reactive metabolite interacted with DNA.
Researchers are still working to determine which biomarkers are most useful for individual toxins, which biological samples provide the most meaningful information, how long different biomarkers remain detectable and how their concentrations relate to actual exposure.
Those questions will be critical before biomarker testing can move from research into routine veterinary practice.
Biomarkers Are Not Ready to Replace Feed Testing
As researchers continue to establish how these biomarkers behave, how long they remain detectable and how their concentrations relate to actual exposure, animal-based testing could eventually provide veterinarians with another tool for investigating suspected mycotoxin exposure. The potential is clear, but the research is not yet at the point where blood or urine mycotoxin concentrations can be used as diagnostics.
Both studies point to the need for more longitudinal research. Repeated measurements of biomarkers alongside feed contamination, animal health and performance would help to determine how internal exposure changes over time and whether those changes are associated with meaningful biological effects.
For now, biomarkers should be viewed as another way of looking at mycotoxin exposure, rather than a replacement for feed analysis.
Feed testing can identify potential exposure in the ration. Biomarkers ask a different question: Is there evidence of that exposure inside the animal?
The future may not be about choosing between testing the feed and testing the cow. It may be about using both to build a clearer picture of what’s happening.
