ENGLISH VERSION notably because climate change is encouraging the establishment of new plant species in their environment. Horse owners ' lack of botanical knowledge is also a risk factor.
For a long time, people believed that horses pulling hearses were victims of a curse. Tied up at the entrance to cemeteries, they would suddenly collapse and die on the spot or a few hours after a burial. Such a phenomenon was bound to fuel every superstition imaginable. Its repeated occurrence, as impressive as it was mysterious, ultimately led to the discovery of the toxicity of the yew tree, a non-resinous conifer commonly found in cemeteries. The European yew is toxic to most mammals, including humans, but the lethal dose for a horse is particularly low: ingesting just 100 to 200 grams of needles is enough to fatally poison a 500-kilogram horse within minutes or a few hours. When the first symptoms appear— even after a smaller intake— it is generally too late to initiate effective treatment. Gastric lavage, administration of activated charcoal or paraffin oil, intravenous fluids, and medications aimed at preserving cardiac function may all be attempted. However, the prognosis is usually extremely poor. Although yew trees are not naturally present in pastures, they are frequently used for ornamental and landscaping purposes. They may therefore be planted in private gardens, competition venues, parks, and other public spaces. A horse tied nearby may nibble on the tree out of boredom, just as the hearse horses once did, with the fatal consequences we now understand.“ A trail rider, for example, must carefully choose where to tie up their horse during a break and check that there are no toxic plants nearby,” explains Nelly Genoux, an agronomist whose extensive botanical expertise benefits her employer, the French Horse and Riding Institute( IFCE). Her mission is to popularize scientific knowledge and make it accessible to the general public, who are often unfamiliar with the plant kingdom.“ The idea is not to frighten people but to help them identify plants and understand the main risk factors,” says this photography enthusiast, who documents plant species that are harmful to equines. Because protecting a horse from dangerous plants first requires being able to recognize them. Yet contemporary Western society, predominantly urban, has become increasingly disconnected from nature and no longer knows how to“ read” it. Some poor practices even stem from good intentions.“ A walker who sees a horse in a field with little grass may feel tempted to pull up a random clump of vegetation from a ditch and offer it to the animal. But it could very well be a toxic plant,” warns Nelly Genoux.
Exotic or imported species are often harmful to horses. Oleander, for example, originally from the Mediterranean basin but now widespread throughout France, is highly toxic. Just 25 grams, roughly ten leaves, can kill a horse. Another example is the box elder maple( Acer negundo), introduced from the United States in the 18 th century to beautify parks and gardens. It is now considered an invasive species and is the target of eradication campaigns in southwestern France. Its seeds and seedlings are just as toxic as those of the sycamore maple, as they contain an amino acid called hypoglycin A, which causes atypical myopathy, a frequently fatal disease that destroys postural muscles, respiratory muscles, and the myocardium.“ Maple seeds are easily carried by the wind and can contaminate a horse’ s environment even when the tree itself is not present nearby,” notes Nelly Genoux.
The Great Vintages of Poison Some plants are deadly in very small quantities but are rarely encountered in our environment. Others, far more common in our regions, gradually deliver their poison over time, with small doses accumulating until they ultimately cause serious, and sometimes fatal, disorders. Ragwort species, herbaceous plants with yellow flowers related to the dandelion, act in this way, quietly and insidiously. Consuming
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