Rats and mice are often an issue in barns, and since many rodenticides are grain-based, they are attractive to horses. Rodenticides placed in barns should be in a secure rodenticide bait station to minimize the risk of nontarget species ingesting the bait. The ASPCA Animal Poison Control Center (APCC) often receives calls about how to treat horses who have accidentally ingested rat or mouse poisons. For any potential rodenticide intoxication, accurate identification of the specific type of bait ingested is key to appropriate and successful treatment. Ingredients from the bait should be taken from the original packaging whenever possible. Treating for all three kinds of bait is appropriate when the active ingredient of the bait cannot be definitively determined.
Anticoagulant rodenticides interfere with vitamin K recycling by inhibiting vitamin K epoxide reductase. This prevents vitamin K from being reused and leads to a deficiency. Since vitamin K is required for the production of clotting factors (II,VII, IX, and X), a deficiency is problematic. The dose of concern for horses is not well established and may vary between baits. For second and third-generation anticoagulant rodenticides, a conservative level of concern would be 0.02 mg/kg. Partial thromboplastin time (PTT) should be checked at 24 and 48 hours after exposure. Vitamin K1 is the antidote. It can be given either if the PTT is increased or can be started prophylactically if PTT is not available at a dose of 2.5 mg/kg PO, SQ or IM twice daily. Treatment for a warfarin bait would be 14 days, bromadiolone for 21 days, and all other anticoagulant rodenticides should receive vitamin K1 for 30 days. Vitamin K3 should never be given to horses due to the potential to develop nephrosis. A PTT test should be performed 24-48 hours after the last dose of treatment.
Bromethalin is a neurotoxic rodenticide. There is no published data about the level of concern for bromethalin in horses. It would be unlikely that most horses would have access to enough bait to cause toxicosis. However, as there is no treatment once signs occur, decontamination may be considered for horses that get into a substantial amount of bait. Multiple doses of activated charcoal may be needed depending on the dose.
Cholecalciferol rodenticides can cause hypercalcemia, hyperphosphatemia, and acute kidney injury when enough is ingested to cause toxicosis. The dose of concern for horses starts at 0.35 mg/kg. At dosages that can cause toxicosis, renal values and serum or ionized calcium should be monitored out to 96 hours after exposure. Decontamination with activated charcoal should be considered for recent exposures. Treatment consists of the management of hypercalcemia and hyperphosphatemia to prevent tissue calcification and damage, especially to the kidneys.
For assistance in managing rodenticide exposure, the ASPCA Animal Poison Control Center is available 24/7 at (888) 426-4435.