Maladie de l’herbe – Etiologie possible au Royaume-Uni
Iron and heavy metals in forage have been implicated in a British study as a cause of equine grass sickness [EGS].
Research conducted by a team from the School of Pharmacy at the University of London found significantly higher levels of iron and heavy metals in herbage growing in sites prone to equine grass sickness, as well as an abundance of toxic buttercups.
Their findings, published in the journal, Frontiers in Pharmacology, also indicated that cyanobacteria in drinking water are unlikely to be a factor as they were absent in the samples analysed.
The findings suggest that the presence of 2 or more causative factors could be the trigger for an outbreak of the disease, and the combination of both seems to be a key predictor.
Equine grass sickness, not to be confused with ryegrass staggers, is a dangerous disease of horses, ponies, and donkeys. With a mortality rate of more than 90 per cent, researchers are desperate to find a way of stopping the illness, first identified in Scotland more than 100 years ago. The disease, also known as equine dysautonomia, occurs throughout northern Europe, but particularly in Great Britain. It primarily affects animals between the age of 2 and 7 years who are pasture-grazed.
Visible signs include colic, difficulty in swallowing, drooling, muscle tremors, rapid weight loss, and behavioral abnormalities. The disease causes impaired intestinal activity as a result of damage to the autonomic nervous system.
While there have been several scientific studies investigating the disease, the causative agents have remained speculative, hindering efforts to develop diagnostic testing and treatment.
It is likely that the disease is linked to elements of the animals’diet, either in the food or the drinking water.
“Previous studies have implicated anaerobic bacteria, notably _Clostridium botulinum_, but what triggers the severe bacterial infestations remains enigmatic,” the London researchers noted.
“We hypothesized that a detailed comparison of soil mineral and botanical composition of equine grass sickness and control sites would yield new insights into the causation of the disease.”
The research team analyzed soil, plant, and water samples from a total of 23 sites where horses were prone to equine grass sickness and 11 control sites.
“Significantly, equine grass sickness sites had higher levels of soil nitrogen, and significantly higher levels of iron, lead, arsenic, and chromium in the herbage,” the researchers said.
“Toxic _Ranunculus_ spp. (buttercups) were found in abundance at every EGS site, making ingestion plausible.
“Conversely, neurotoxin-producing cyanobacteria were not found in any of the water samples analyzed.
The significantly higher levels of iron and heavy metals found in herbage growing at the grass sickness sites, in addition to toxic buttercups, suggested previously unknown triggers were involved,” they said.
Britain has had a national surveillance scheme in place for the disease since 2006.
April to June is predominantly the time when the number of equine grass sickness cases peak in Britain.