Food For Thought Horse Series: Garlic and Horses:
- naturalhorse1
- Sep 15, 2021
- 4 min read
Updated: Mar 14
Garlic can cause anaemia in horses due to compounds such as N-propyl disulfide and other organosulfur compounds that damage red blood cells. While garlic is sometimes fed to horses as a natural insect repellent, it can cause toxicity and anaemia, particularly when fed in larger quantities.
Many years ago, while researching plant toxicities in horses, I came across information showing that garlic can cause serious health problems for our equine friends. It is directly associated with a condition known as Heinz Body Anaemia, which can then lead to hemolytic anaemia.
Heinz bodies form when haemoglobin within red blood cells is damaged by oxidative stress. Instead of functioning normally, the haemoglobin clumps together inside the red blood cell, forming small inclusions called Heinz bodies. These damaged cells are then recognised by the body and removed, or they rupture prematurely.
Garlic contains compounds called thiosulfates that can trigger this oxidative damage.
As more red blood cells become damaged and destroyed, the horse can develop haemolytic anaemia. This means the red blood cells are breaking down faster than the body can replace them. Red blood cells are responsible for carrying oxygen around the body, so when they are damaged or destroyed, the horse’s ability to deliver oxygen to tissues is reduced. This can lead to weakness, lethargy, reduced performance and in more serious cases, additional strain on organs such as the liver.
In the image shown, the Heinz bodies appear as dark inclusions attached to the red blood cells.
Garlic affects horses differently than it affects humans because horses are particularly sensitive to oxidative damage in their red blood cells. Compounds in garlic, including thiosulfates and related organosulfur compounds, damage the haemoglobin inside equine red blood cells. When this happens, the haemoglobin forms Heinz bodie,s which weaken the structure of the cell and cause those red blood cells to be removed or destroyed prematurely.
Humans can eat garlic without experiencing this effect because our bodies process these compounds differently. Horses do not have that same tolerance, so repeated exposure or larger amounts can lead to oxidative damage and Heinz Body Anaemia.
Despite this information being publicly available for many years, garlic is still widely marketed and sold for horses. It appears in supplements, feed mixes, licks, sprays, herbal remedies, tinctures and pelleted feeds.
Many people associate garlic with health benefits for humans when consumed in small amounts. Because of that, some assume garlic must also be beneficial for horses. Unfortunately, horses do not share the same physiology, and what may be tolerated by humans does not automatically translate safely to the equine digestive and blood systems.
Scientific research has shown that Heinz Body Anaemia can be induced in healthy horses when freeze-dried garlic is fed at relatively small doses.
In one study, horses fed approximately 0.05 g of freeze-dried garlic per kg of body weight, which equates to roughly 25 g per day for a 500 kg horse developed Heinz body anaemia. The researchers themselves concluded that further work was required to determine whether a truly safe feeding level exists.
So when we look at the science and the fact that Heinz Body Anaemia has already been induced in healthy horses in controlled studies, it raises a very simple question.
Why risk it?
Because of these negative associations with garlic, we would strongly advise caution and recommend avoiding feeding garlic to horses until we truly understand safe dose thresholds. At this stage, it is clear that much more research is needed before we can confidently say what amount, if any, is safe.
Our horses depend entirely on the decisions we make for them. When there is credible evidence showing a potential risk, the safest option is usually the simplest one.
We hope this helps you make a well-informed decision when feeding your horses.
Here is the abstract from the research paper where horses were fed approximately 0.05 g per k,g which equates to around 25 g per day
Another study showing altered blood parameters
Additional research
For a comprehensive horse feeding plan that does not include garlic, please see
Happy Horsing
References
Rahman M.S. Allicin and other functional active components in garlic Health benefits and bioavailability. Int J Food Prop 2007 10 245–268
Pearson W, Boermans H.J., Bettler W.J., McBride B.W., Lindinger M.I. Association of maximum voluntary dietary intake of freeze dried garlic with Heinz body anemia in horses. Am J Vet Res 2005 66 457–465
Williams C.A., Lamprecht E.D. Some commonly fed herbs and other functional foods in equine nutrition A review. Vet J 2008 178 21–31
Borrelli F., Capasso R., Izzo A.A. Garlic adverse effects and drug interactions in humans. Mol Nutr Food Res 2007 51 1386–1397
National Academies of Sciences. Safety of Dietary Supplements for Horses Dogs and Cats. National Academies Press 2008
Hu Q., Yang Q., Yamoto O., Yamasaki M., Yoshihara T. Isolation and identification of organosulfur compounds oxidizing canine erythrocytes from garlic. J Agric Food Chem 2002 50 1059–1062
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