Environmental influences on mare reproductive loss syndrome: Do they fit with a toxin as the causative agent?

This research paper investigates whether the Mare Reproductive Loss Syndrome (MRLS), a term for abortions in mares in connection with Eastern Tent caterpillars, can be attributed to toxins. Its findings suggest that both environmental factors and a potential toxin could be contributing to the occurrence of MRLS.

Hypothesis and Testing Mechanism

• The researchers hypothesised that a toxin might be the cause of MRLS. They tested this hypothesis by using Westerman’s Correlates of Causal Strength of Evidence (WCCSE), a method for evaluating the strength of evidence in supporting a particular causal connection.
• Upon testing, the hypothesis that a toxin could be causing MRLS was found to be consistent with all correlates examined through WCCSE.

Role of Environmental Factors

• The researchers looked into environmental factors that could be contributing to MRLS. They found these factors to also be in line with the toxin hypothesis.
• Instances of MRLS were found to be associated with higher than normal temperatures and lower than normal rainfall. The researchers explain that increased temperatures, coupled with lower rainfall, facilitate a greater population density of Eastern Tent Caterpillars (ETCs) in a specific timeframe.
• This encourages these caterpillars to ingest more Black Cherry tree leaves, which contain prunasin – a precursor to the suspected toxin. The prunasin defends the caterpillars from predators.

The Role of Eastern Tent Caterpillars (ETCs)

• ETCs are seen to act as the vector for the toxin, contaminating pasture and water when they feed off-tree. During periods of low rainfall, the toxin accumulates on the pasture, increasing exposure and clinical responses.
• When it rains, the contaminants are diluted, reducing the toxin dose and clinical effects after the contaminated grass or water has been ingested.

Conclusion

• Even though the exact cause of MRLS remains unproven, the researchers conclude that the potential role of a toxin should not be overlooked. The combination of the toxin, its carrier (ETCs), and environmental factors produce a scenario that fits the symptoms and occurrences of MRLS.