Toxicosis from agricultural chemicals

Most agricultural chemicals that horses are exposed to are pesticides. Toxicosis from pesticides is infrequent in horses and is usually the result of inappropriate use, handling, or storage. Most herbicides have low toxicity in mammals, especially if the dilution rate, application rate, and re-entry times are observed. However, some herbicides can alter the toxicity of poisonous plants. Herbicides that contain arsenic or chlorates are the most toxic. Pentachlorophenol is a fungicide and wood preservative that can be contaminated with dioxins. Horses develop a chronic wasting syndrome and significant skin lesions. Some pesticides are marketed in a pelleted form that may contain grains, which are readily consumed by horses. Metaldehyde is a molluscicide that affects the nervous system. Strychnine also affects the nervous system. Zinc phosphide is a rodenticide that is converted into a toxic gas in the horse's stomach and can be toxic to humans as well. The organophosphorus and carbamate insecticides are acetylcholinesterase inhibitors, the insecticide class most frequently associated with toxicosis. The most recognizable signs of toxicosis are the “SLUD” signs, but some of these insecticides, as well as the organochlorine insecticides, can cause seizures.