Affected animals (not all animals are equally affected) develop clinical signs of fever, dermal edema, varying clinical chemistry
depending on the organs affected and finally failure of organs and systems affected (skin, lymph node, lungs, kidneys, liver,
heart, gastrointestinal tract, skeletal muscle and eyes). Poisoning usually is fatal. Because there is no proven treatment
and the disease is irreversible, avoiding exposure is essential.
Toxic plants are a significant health concern for horses. Most poisoning occurs when hay and prepared feeds are contaminated.
Caution should be exercised in buying hay to ensure that it is safe and of good quality.
Because most weed infestations are patchy, the best way to do this is to inspect the hay field before it is harvested. Hay
should also be closely inspected prior to feeding it.
Less commonly, horses can be poisoned when they are pastured with toxic plants with limited alternative forages. Most of these
poisonings can be prevented by monitoring pasture and grazing animals.
Because many poisonings can cause permanent damage, avoiding exposure is best. Knowledge of which plants are toxic and when
horses are likely to be poisoned also will help reduce these losses and ensure animal health and safety.
Dr. Stegelmeier is a researcher at the U.S. Department of Agriculture's Poisonous Plant Research Laboratory in Ogden, Utah.