While you may feel over-dramatic or abnormally paranoid if you suspect your horse has been poisoned, it can happen. Poisoning conjures up images of a desperately ill horse in a life-threatening situation, but chronic toxicities occur, too, and initial symptoms aren’t necessarily dramatic.
Our table (see sidebar) lists some of the more common and/or dangerous poisonous plants/trees, and the symptoms of poisoning. It’s important to realize that symptoms often refer to only acute poisonings, or the latest stages of chronic poisonings. Many horses can be poisoned without showing all symptoms. Most people know about moldy corn poisoning, a fatal fungal toxicity, but there are probably many more horses than is recognized being sickened by chronic ingestion of mold-contaminated hays or grains.
Chronic exposure to chemicals is possible from multiple sources, including natural water supplies. Many streams and rivers are so polluted that local governments have issued warnings about eating fish caught in them. You don’t have to be paranoid about the occasional drink along the trail, but if you’re using untreated well or natural water sources as your horse’s main water supply it would be wise to have them tested.
The symptoms of poisoning vary on the specific poison/toxin, as well as dose, and what body systems the poison attacks--the nervous system, digestive tract, urinary system, circulatory system--so the only thing that applies across the board to all poisonings is “Sick Horse.” With acute, high-dose poisonings, a very sick horse is likely, but with slower poisonings it’s often difficult to even put your finger on any specific symptoms beyond “horse not doing well.”
Many poisonings get missed because your veterinarian will probably concentrate on ruling out more likely causes of the symptoms. For example, a horse showing nervous-system signs will have viral encephalitis, EPM, rabies and botulism suspected before a poisoning. There’s nothing wrong with this, and diagnostic workups are supposed to start with the most likely causes first, but when it’s actually a poisoning valuable time may be lost.
You can help avoid delays in diagnosis by knowing, and being on the look out for the dangers in your area (also see Minimizing Your Risk), and by being very observant of changes in your horses such as:
• Behavior changes
• Change in manure or patterns of urination
• Colic or salivation
• Change in appetite
• Unexplained weight loss
• Change in level of activity
• Balance/movement problems
• Coat/skin changes
• Decreased exercise tolerance
• Unexplained leg problems
• Poor growth in young horses.
Things that may seem minor at one time can be important clues later on. Symptoms may even be different in different horses (and not all horses affected), so be sure to report to your vet everything you have observed.
Finally, realize that a horse may show symptoms that haven’t been reported yet as specific to that poisoning. With many chemical exposures, we don’t even know what to expect as far as symptoms. You know your horse best. If you think something is wrong, call your veterinarian. Even if the actual problem is never identified, she/he can help you make changes in management that eliminate possible poisonous exposures.