Rats and mice are often an issue in barns, and since many rodenticides are grain-based, they are attractive to horses. The ASPCA Animal Poison Control Center (APCC) often receives calls about how to treat horses who have accidentally ingested rat or mouse poisons. Because there are several different types of rodenticides and identification is key for proper treatment, the APCC recommends the following.
Anticoagulant rodenticides interfere with vitamin K, the component required for production of clotting factors (factors II, VII, IX, and X). Because these factors are consumed in normal maintenance of body functions, the lack of vitamin K recycling will lead to coagulopathy. There are few published doses of concern for horses, so like other mammals, dose of 0.02 mg/kg or above require monitoring. The horse’s PTT can increase as early as 24 hours post-exposure. Vitamin K1 is the antidote and can be given at a dose of 2.5 mg/kg twice daily for 21 to 30 days, depending on the rodenticide ingested. For the first three days, Vitamin K1 should be given subcutaneously or via the intramuscular route, and starting on the fourth day, treatment can be given by mouth. PTT test should be repeated 24-48 hours after the last dose of treatment.
Bromethalin is a neurotoxic rodenticide. The concentration of bromethalin in most baits is 0.01%. There is no published dose of concern for bromethalin in horses. The dose of concern for sensitive species is 0.05-0.1 mg/kg and above. It would require large amounts of bromethalin to become a concern in the horse due to the low concentration in the available rodenticides. There is no treatment once CNS signs have developed, so decontamination is the only option with suggested treatment for any exposure involving a 0.1 mg/kg dose and above. Multiple doses of activated charcoal may be needed depending on dose.
The newer cholecalciferol rodenticides can be a potential risk with very large ingestions. Cholecalciferol rodenticides are found at 0.075% strengths. At doses over 0.35 mg/kg in the horse , it’s critical to start monitoring the renal values and the calcium levels. Treatment often involves decontamination with activated charcoal if the exposure is within the first 12 hours. If longer than this, calcium, phosphorus and renal values should be monitored every 24 hours for 4 days. Treatment involves management of renal failure and the hypercalcemia that accompanies vitamin D toxicosis.
Talking with horse owners about the proper storage of rodenticides can prevent these dangerous exposures from happening. For assistance in management of rodenticide exposure, ASPCA Animal Poison Control is available 24 /7 at (888) 426-4435.