Liver disease is a relatively common problem in horses. The liver is the main organ involved in the accumulation, metabolism and distribution of nutrients within the body. The majority of nutrients absorbed from the gastrointestinal tract pass via the portal circulation directly to the liver where they are metabolized, repackaged and either stored or exported to peripheral tissues.
Horse grazing in a field of mixed hay and grass forage.
Several mycotoxins with known hepatotoxic potential were found at case premises, consistent with the hypothesis that forage-associated mycotoxicosis may be a cause of liver disease in horses.
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The liver also has a vital role in detoxification of both endogenous and exogeneous substances. The liver acts as the ‘first line of defence’ for all toxic substances that are absorbed via the gastrointestinal tract.
As a result of this, the liver can be injured by many substances that are absorbed within the horse’s diet. The presence of gastrointestinal disease with intestinal inflammation can also cause injury to the liver.
Mycotoxins are an important and often underestimated cause of liver disease in horses. Mycotoxins are harmful substances that are produced from moulds growing on crops either during growth, harvesting or storage. Environmental conditions can have a huge impact on the levels of toxins produced.
Increased amounts of these substances are produced during times of ‘stress’ for example extremes of temperature, dry weather etc. Once produced, these toxins are very stable and survive on pasture/forage for long periods of time.
Outbreaks of liver disease in horses are common but the etiology of most remains unknown. Forage mycotoxins have been suspected to be a cause. A recent study in the United Kingdom examined the association between outbreaks of liver disease and the presence of mycotoxins in forage stored on the same premises.
For the study premises were identified where ≥4 horses were contemporaneously affected by liver disease, and a control group was formed from premises where ≥4 horses had been examined and found to have no evidence of liver disease.
Forage was collected from 29 case and 12 control premises. The forage was analyzed for mycotoxin content using a liquid chromatography/mass spectrometry method, targeting 54 mycotoxins. The presence and distribution of mycotoxins between case and control samples was compared.
Mycotoxins were found in 23/29 (79%) of case samples and 10/12 (83%) of control samples (P > .99; relative risk, 0.93; 95% confidence interval [CI], 0.64-1.75). Median (interquartile range [IQR]) total mycotoxin concentration was similar in case and control samples (85.8 μg/kg [1.6-268] vs. 315 μg/kg [6.3-860]; P = .16). Ten mycotoxins were found exclusively in case premises comprising fumonisin B1, 15-acetyldeoxynivalenol, deoxynivalenol, zearalenone, aflatoxins B1 and G1, methylergonovine, nivalenol, verruculogen, and wortmannin. The median (IQR) concentration of fumonisin B1 was significantly higher in case versus control samples (0 μg/kg [0-81.7] vs. 0 μg/kg [0-0]; P = .04).
Conclusions and clinical importance: Several mycotoxins with known hepatotoxic potential were found, alone or in combination, exclusively at case premises, consistent with the hypothesis that forage-associated mycotoxicosis may be a cause of outbreaks of liver disease in horses in the United Kingdom.
Article by Andy E Durham with minor editing by EquiMed
Press Relese by Ontario Animal Health Network