Discussion
There is very little published data investigating mycotoxin level in
forage in the UK. It is well documented that the source of mycotoxin
feed contamination is more likely to originate from processed grains or
feed than grass or hay that undergoes little or no storage or processing
(Krizova et al. 2021). Mycotoxins are often not homogenously dispersed
in the feed and this problem is even more apparent when sampling grass
across a field (Skladanka et al. 2013). Mycotoxins may therefore stay
analytically undetected, even with perfect sampling procedures (Binder
2007). However, the risk of mycotoxin-contaminated forage has been
documented (Raymond 2000; Durham 2022), and confirmed in this study,
where mycotoxins were identified in 96% of forage samples.
This paper made no attempt to draw causation between mycotoxin ingestion
and increased liver enzyme concentrations. There are many and complex
reasons for increased liver enzyme concentrations including ingestion of
mycotoxins (Raymond et al. 2003; Durham 2022). We included samples from
horses with increased liver enzyme concentrations to identify mycotoxins
that may have some clinical relevance for horses and to guide further
research, not to draw associations between the mycotoxin exposure and
liver disease where a control group would be necessary.
The most commonly detected mycotoxin group was emerging mycotoxins,
found in 75% (39/52) of samples. However, when identified, emerging
mycotoxins were found at concentrations that are not considered a risk
to equine health. This contrasts with type B trichothecenes, which
although identified in 46% (24/52) samples, was more commonly found at
significant concentrations. In 8/24 samples type B trichothecenes were
identified at medium or high-risk concentrations. Type B trichothecenes
are produced by fusarium moulds and are frequently identified in forage
in Europe (Pereira et al. 2019). They can cause significant
gastrointestinal disease in humans and pigs from both acute and chronic
exposure (Pinton and Oswald, 2014). Feed refusal and gastrointestinal
erosions have been noted in pigs after chronic exposure to
deoxynivalenol (DON), which is a type of Type B trichothecenes (Pinton
and Oswald, 2014). DON was found more commonly in colic cases compared
to the control group in one study (Dänicke et al. 2021). In a study by
Raymon et. al in 2003, the impact of fusarium mycotoxins fed to horses
(DON (14,000 ug/kg), fusaric acid (6400 mg/kg) and zearalenone (2000
ug/kg)) was demonstrated by a significant reduction in feed consumption
and GGT significantly increased compared to control day 7-14 (Raymond et
al. 2003). They concluded that exercised horses are also susceptible to
fusarium mycotoxicosis as indicated by appetite suppression and weight
loss when feeding contaminated feed with fusarium mycotoxins for 21 days
(Raymond et al. 2005). Whilst these studies demonstrated clinical
effects of significant fusarium exposure in horses, no histology was
performed, and study duration was limited to 21 days. More research is
needed to establish subclinical effects as well as the effects of longer
exposure and lower doses.
The lack of a control group was a significant limitation of the study.
Previous studies identifying mycotoxin exposure of horses with colic and
liver disease, also identified mycotoxins in control populations
(Dänicke et al. 2021; Durham 2022). Whilst we cannot conclude in this
study if the increased liver enzyme concentrations were related to the
mycotoxin exposure, it has demonstrated the frequency at which
mycotoxins are identified in UK forage. Despite being found in control
populations in other studies, there is insufficient data to conclude
that mycotoxins are not potentially significant to equine health.
Exposure to high levels has been demonstrated to cause acute disease,
but no long-term cohort studies have been performed in horses to assess
long term consequences (Raymond et al. 2003; Raymond et al. 2005).
No studies have quantified the cumulative risk of multiple mycotoxins on
horse health. Moulds can produce multiple mycotoxins and there is
evidence of the synergistic effects of fusarium mycotoxins
(Alassane-Kpembi et al. 2017). Adverse performance risks associated with
multiple mycotoxin in feed can be evaluated in farm animals to calculate
a risk equivalent quantity (REQ) (Yiannikouris, 2013). In this study,
40/52 samples had two or more groups of mycotoxins detected and 25/52
samples had a medium or greater REQ. This suggests that the number of
mycotoxins identified should be considered in addition to the type and
concentration of mycotoxin detected. However, further work is needed to
establish both the effects of individual and multiple mycotoxins on
horses.