Certain mycotoxins identified in stored hay have been linked to some cases of liver disease in horses.
While the British study reported, in Journal of veterinary internal medicineWhile mycotoxins have not been shown to cause liver disease in horses, the results provide a basis for further investigation of potential links.
Study author Professor Andy Durham, Clinical Director at Lieboke Equine Hospital in England, noted that in most outbreaks of liver disease in horses, the cause remains elusive.
“Many fungi produce metabolites that possess antibacterial, antiviral, antihelminthic, antifungal, herbicide and insecticidal properties, which may provide a competitive advantage,” he said.
Some fungal products are also toxic to mammals. More than 500 of these mycotoxins have been identified, mostly from fungi of the genera Aspergillus, Penicillium, Rotation and Fusarium. He noted that mycotoxins are also a major human health concern, with about 25% of global crop production being contaminated.
Monogastric species, including horses, are more susceptible to mycotoxins than ruminants, with major groups threatening animal health including aflatoxins, ochratoxins, trichothicins, fumonisin and zearalenone.
He said several mycotoxins are known to be linked to liver disease.
In his study, Durham set out to examine the relationship between outbreaks of liver disease in horses and the presence of mycotoxins in feed stored in the same building.
Loci of four or more horses with liver disease were identified at approximately the same time, and a control group was formed from loci in which at least four horses were examined and found, on the basis of serological analysis, no evidence of liver disease.
To meet the study criteria, cases of liver disease in affected horses must be confirmed concurrently by either serum biochemistry or liver biopsy, and without establishing a cause.
Forage was collected from 29 buildings that met the condition criteria and 12 buildings for observation.
The forage was analyzed for mycotoxins using liquid chromatography/mass spectrometry, targeting 54 mycotoxins. The presence and distribution of mycotoxins were compared between case and control samples.
Mycotoxins were found in 23 out of 29 hay samples of hepatotoxic properties, which accounted for 79% of the samples. and 10 out of 12 control samples, representing 83% of the samples. Mean total mycotoxin concentrations were similar between the two sample groups.
However, 10 mycotoxins, alone or in combination, were found exclusively in the case loci: fumonisin B1, 15-acetyldeoxynivalenol, deoxynivalenol, zearalenone, aflatoxins B1 and G1, methylergonovine, nivalenol, verruculogen and wortmannin. Many of them have the potential to cause liver disease.
He said the findings were consistent with the hypothesis that feed-associated fungal poisoning may be a cause of outbreaks of liver disease in horses in Britain.
Durham said that mycotoxins were present in more than 80% of the hay samples tested across all buildings, although neither the overall prevalence nor the total mycotoxin concentrations differed between hay fed to horses with liver disease versus those in the control settings.
The difference lies in the ten mycotoxins that are found exclusively in liver disease sites, suggesting that they can be considered as possible causes.
Among these, fumonisin B1 was the most prevalent and differed significantly between the case sample and the control sample.
The most common mycotoxins identified via straw samples were fusaric acid, ochratoxin A, fumonisin B1, penicillic acid, and neosolaniol. However, the only mycotoxin found in feed taken from case facilities at concentrations much higher than in control samples was fumonisin B1.
“In contrast, fusaric and penicillic acids were found in significantly greater amounts in the control hay samples, with ochratoxin A nearly reaching significance.”
This finding may reflect storage and growth factors that favor the production of specific mycotoxins with and without the potential to cause liver disease.
He said mycotoxin contamination is known to vary greatly for the same crop in different years, depending on factors such as local temperature and humidity.
Interestingly, although fusaric acid, penicillic acid or ochratoxin A was present in 20 of 41 straw samples, only one of the nine fumonisin B1-positive samples contained fusaric acid (the lowest amount detected of all samples) and did not. Which ones contain penicillic acid or ochratoxin A? This may indicate important differences in hay storage standards in canister locations and monitoring.
Durham said the adverse health consequences of mycotoxins can be complex and unpredictable. They depend on a combination of factors, including animal species, bioavailability, and co-exposure to other mycotoxins.
“In addition to fumonisin B1’s association with liver disease in our study, it is possible that other mycotoxins also have a pathogenic link.”
Durham raised several limitations to his study but said the findings provide a basis for further study of some mycotoxins.
He said it was unlikely that those found more commonly in surveillance settings were related to liver disease outbreaks. Alternatively, focusing on other mycotoxins, such as fumonisin B1, might make more sense.
Durham, United Arab Emirates, Association between feed mycotoxins and liver disease in horses. J Vet Intern Med. 2022; 36 (4): 1502–1507. doi: 10.1111/jvim.16486
The study published under CC licensecan be read over here.