Garlic and Horses

Many horse owners have recently been asking about giving their animals herbs or natural supplements, specifically garlic.  They have heard that it can help with fly and worm control, pain relief, treatment of infection, and many more issues.  The problem with feeding garlic to horses is that horses will willingly consume toxic amounts.  Research shows that a toxic amount is more than 0.2 mg/kg of their body weight.  This is only .003 ounces in a 1000 lb horse.  These amounts have caused Heinz body anemia during times of consumption.  Heinz-body anemia is a complicated process.  The toxic element in garlic and onions is a chemical called N-propyl disulfide.  By altering an enzyme present within the red blood cell, it depletes the cell of a chemical known as phosphate dehydrogenase (PD), whose job is to protect the cell from natural oxidative damage.

When the PD level gets low enough, the hemoglobin in the cell oxidizes and forms a bubble called a Heinz body on the outside of the cell.  This Heinz body is distinctive and able to be seen under the microscope. The spleen quickly removes the deformed red cell from the bloodstream. As more and more red cells are prematurely damaged and removed, as happens from consistent poisoning with N-propyl disulfide, horses gradually becomes anemic.

Toxic effects are more gradual but still very dangerous when a lower dose is consumed on a regular basis, resulting in a mild anemia without obvious symptoms.  Some cases of Heinz-body anemia occur every year in horses that graze on wild onions or garlic growing in their pastures.  Depending on the dose, and the frequency and duration of dosing, there could be low-grade damaging effects, due to red-blood-cell damage that's not enough to cause an emergency situation, but just enough to cause a mild anemia that might not be outwardly evident.  It might affect your horse's stamina, energy level, or resistance to disease.

Recovery from anemia may not occur until after 5 weeks following termination of dietary supplementation with garlic.  Research further suggests that the only real benefit of feeding garlic to horses is that it may increase concentrate consumption.  Since most horses readily consume plenty of concentrate anyway, there is little reason to add garlic to an animal’s diet. 

The potential for garlic toxicosis also exists when horses are chronically fed garlic.  Animals are not able to digest garlic like people can, which is why a buildup occurs.  Symptoms of garlic toxicity include trouble breathing, lethargy, diarrhea, vomiting, an elevated heart rate, an increased respiratory rate, weakness, and collapse.

Most herbs have not been scientifically tested for use in animals.  It is therefore unknown if they are safe or even effective.  They are also not regulated with the same scrutiny as conventional drugs.  Some commonly found supplements fed to horses other than garlic include:  Echinace, ginger, ginseng, peppermint leaf, and yucca.  Some herbs have drug-like actions that interact with dietary components.  Drug-herb interactions are common and caution needs to be taken when implementing natural product usage.

Anytime you are thinking about introducing new supplements or a home remedy treatment for your animals, always consult your veterinarian first.  If you need help finding a balanced ration for your horses, please call your local Livestock Agent.