An attempt to reproduce ‘mal seco’ in horses by feeding them Festuca argentina.

This study attempted to replicate ‘mal seco’, a fatal horse disease prevalent in Argentina and Chile, by feeding three horses with the presumed toxic plant Festuca argentina. However, the results did not provide clear evidence that the plant alone causes the disease, suggesting that other factors may also be at work.

Objective of the Research

• The purpose of the study was to investigate the cause of ‘mal seco,’ a near-universally fatal disease that afflicts horses in Argentina and Chile. The disease bears similarities to grass sickness, a type of horse dysautonomia found in Europe.
• Specifically, the researchers wanted to find out if Festuca argentina, a plant which is considered toxic to animals and frequently found in the diet of mal seco-affected horses, is the cause of the disease.

Methodology

• Three horses were fed with Festuca argentina ad libitum for 28 days. The plant was infected with an endophytic fungus, Acremonium chlamydosporioides, which research suggests may be a contributing factor.
• Throughout the duration of the study, the health conditions of the horses were closely observed for any signs of mal seco.

Results and Findings

• Of the three horses, two did not display any clinical abnormalities. However, one of the horses died on the fifth day showing symptoms of incoordination, unsteadiness, and ataxia (lack of voluntary control of muscle movements) in its limbs.
• The post mortem analysis did not reveal any significant changes in any of the horses except for the presence of Fasciola hepatica (liver flukes) in the liver of the deceased horse, and Gasterophilus species (a genus of botfly) in the stomachs of all three horses.
• There were no histopathological changes observed in any of the examined organs, which covers several autonomic ganglia, brain, most brain stem nuclei, spinal cord, liver, kidney, stomach, and small and large intestine.

Conclusion

• The results of the investigation suggest that Festuca argentina may not be directly responsible for the onset of mal seco, or that its effects only manifest when triggered by other unknown factors.
• Therefore, further investigation is needed to identify the other potential factors that could be contributing to the incidence of mal seco in horses.