Rat Poisoning in Horses

What Is Rat Poisoning in Horses?

Rat poisoning occurs when a horse ingests a toxic amount of a rodenticide, a poison used to kill rats, mice, and other rodents. The toxic dose and the symptoms experienced by the horse vary depending on the type of rodenticide consumed.

There are three main types of rodenticides commonly used for the control of rats and mice; long-acting anticoagulants, bromethalin, and cholecalciferol:

• Long-acting rodenticides kill rodents by causing internal bleeding.
• Bromethalin rodenticides induce swelling of the brain.
• Cholecalciferol rodenticides cause elevated blood calcium levels, leading to the mineralization of internal organs, particularly the kidneys and heart.  

While these rodenticides are formulated to target rodents, they can have the same effects on horses if ingested at toxic quantities.

How Do Horses Ingest Rat Poison?

Rodenticides are commonly formulated as pellets and small blocks that are similar in size, shape, and texture to horse treats. They may also be flavored with grain or peanut butter to attract rodents—flavors that, unfortunately, also attract horses.

On occasion, horse owners may inadvertently leave buckets or packets of rodenticide in places where horses have access to them. Because horses are curious about bucket contents and are accustomed to eating pelleted foods, they will willingly taste rodenticides if given the opportunity. Such a bucket might contain multiple pounds of rodenticide, which can lead to a toxic ingestion by the horse.

Symptoms of Rat Poisoning in Horses

Ingesting a toxic dose of rodenticide can result in the following symptoms in horses. For all of these rodenticides, symptoms may take several days to develop.

Long-acting anticoagulants may cause the follow symptoms in horses:

• Lethargy
• Weakness
• Trouble breathing
• Decreased appetite
• Collapse or "down horse"
• Unspecified swelling

Bromethalin rodenticides may cause the following symptoms in horses:

• Lethargy
• Depression
• Coordination problems
• Muscle tremors
• Seizures

Cholecalciferol rodenticides may cause the following symptoms in horses:

• Increased thirst and urination
• Muscle stiffness
• Decreased appetite
• Weakness

My Horse Ate Rat Poison. Now What?

The key to a positive outcome if your horse ate rat poison is a fast response. Calling Pet Poison Helpline (855-764-7661) or your equine veterinarian as soon as you become aware of the rodenticide ingestion is critical for treatment of rat poisoning in horses.

If possible, have the packaging from the rodenticide with you when you make the call. Assessing toxicity and the appropriate treatment depends on knowing what rodenticide was consumed.

Pet Poison Helpline is an animal poison control center available 24/7 with a team of veterinary medical professionals who can determine the seriousness of the exposure and direct your next steps. They will partner with your veterinarian to develop a treatment protocol for your horse.

Treatment of Rat Poisoning in Horses

Early decontamination, or ridding the body of the poison as quickly as possible after ingestion, is critical when trying to manage a toxic exposure to rodenticides. If you know or suspect that your horse has consumed a rodenticide, don’t wait for symptoms to develop before seeking veterinary care.

Within the first few hours of ingestion, regardless of which rodenticide was ingested, treatment will focus on getting the toxin out. The veterinarian may pass a tube into the stomach to remove as much of the poison as possible. Activated charcoal or mineral oil may also be administered to help absorb the poison.

Depending on the time since exposure and the type of rodenticide, blood work may be recommended: For long-acting anticoagulants, blood clotting profiles can help assess the level of toxicity. With cholecalciferol poisonings, repeatedly measuring blood calcium levels can help guide treatment protocols.

While there is an antidote for certain rodenticides, such as vitamin K1 for long-acting anticoagulants, unfortunately there are no antidotes for bromethalin or cholecalciferol. Because of this, decontamination plays a crucial role in preventing the onset of poisoning symptoms and potentially fatal consequences.

Fortunately, the prognosis for rat poisoning in horses is generally good if treatment starts before symptoms develop. Once they do, they can take weeks or months to resolve, and treatments can be costly.

Additionally, horses with neurological signs, such as  stumbling when walking (ataxia), muscle tremors, seizures, or weakness, can pose risks to their human caretakers. Prevention and rapid intervention are the best indicators of a positive outcome in cases of rat poisoning in horses. 

Prevention of Rat Poisoning in Horses

To prevent rat poisoning in horses, always store rodenticides in a locked location or in an area that is too small for a horse to access.

Equally important is to practice good barn hygiene to help make the barn less desirable to rodents and thereby minimize the need for rodenticides.

Store grain in containers with fitted lids to minimize rodent access, and always clean up any spilled grain promptly. Keep fabric items in plastic totes or hang them on hooks well above the ground to help minimize rodent nesting, as rodents like to use filling from blankets and saddle pads for bedding. Trash should be taken out regularly, especially empty feed sacks.

If you do have rats or mice, consider using other non-toxic rodent control methods, such as traps. When you do choose to utilize rodenticides in the barn, use bait stations to minimize exposure.

Keep a record of how much rodenticide was placed in each station, as well as the location of each station, to monitor for potential access. This can be helpful in the event that a bait station is broken into, to assess how much rodenticide is missing and how much may have been ingested by the horse.

By implementing these simple yet effective measures, you can significantly reduce the risk of a dangerous exposure to rat poison for your horses.