Supplements targeting joint health are some of the most sought-after dietary supplements for horses, especially due to the high prevalence of joint injuries and deterioration later in life.
But which equine joint supplements actually work and which are all hype? Many of the ingredients often touted for improving joint health have limited research in horses.
And some of the most popular supplements believed to work have been demonstrated ineffective when actually studied in equine populations. (You may be surprised by which ingredients DON’T work.)
That being said, there are some compounds that have been well-researched in horses and demonstrate efficacy for improving metrics of joint comfort, health and function.
In this article, we will review the research behind 8 of the most popular joint supplements for horses and help you decide which are worth your money and which should be avoided.
Equine Supplements for Joint Health
Joints consists of cartilage which connects to bones, acting as padding while encapsulating the joint. Synovial fluid keeps the joint lubricated and limits friction, or wear-and-tear, between the bones. 
As horses age, perform heavy work, or become injured, their joints can become weak and damaged in several ways. The composition of synovial fluid may change, resulting in less lubricant for the joint. There can be inflammation in the cartilage causing it to deteriorate. This can cause significant pain to the horse and hinder performance and comfort. 
When the cartilage of the joint begins to degenerate, the horse might be diagnosed with osteoarthritis. This condition can have several consequences including: 
Reduced training days
Senior or heavily exercised horses are likely to benefit from a supplement that supports joint health. Choosing the right supplement for your horse can be overwhelming. Some factors to consider are the current health status of your horse, other goals (ie. weight gain or loss) and demonstrated efficacy in horses.
Dietary supplements to support joint health may have several mechanisms of action that achieve any of the following: 
Slow the rate of or inhibit enzymes that deteriorate cartilage
Increase capacity for cells called chondrocytes to synthesize collagen and other important proteins
Improve synthesis of hyaluronic acid by synovial cells
Improve synovial fluid composition
Reduce inflammation and/or oxidative stress
Here we provide a summary of the potential mechanisms, bioavailability, safety and efficacy of some of the most popular supplements available on the equine market today. We also rate the ingredients on the strength of the evidence in horses supporting their efficacy or inefficacy.
Before adding any new supplement to your horse’s diet, it is recommended to consult with an equine nutritionist or other equine healthcare professional. You can submit your horse’s diet online for a complementary evaluation and to receive individualized recommendations for your horse.
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Found in alfalfa and grains, methylsulfonylmethane, or MSM, is a readily available natural form of sulfur. It is well-tolerated by horses and is considered one of the safest supplements to add to your equine feeding program.
Sulfur is important in the horse’s diet as a component of glucosamine and collagen which are found in connective tissue and cartilage.
Bioavailability and Safety: MSM appears safe for consumption in a variety of animal models and is relatively bioavailable, although may need further evaluation for horses. 
While naturally present in small amounts in fresh forage and grains, MSM must be supplemented at higher dosages to support beneficial effects.
Efficacy: The use of MSM for joint health in horses still requires more research, but initial studies report positive results.
The available in vitro studies that look at isolated cells in culture show some protective effects against inflammation and degradation of cartilage. Similarly, in vivo studies in mice and rats show benefits with MSM for reducing inflammation. 
While there is currently limited information on MSM and joint health in horses, there are very promising results:
In a 2008 study using horses (8-13 years of age), it was determined that competitive jumping horses experienced increased oxidative stress as identified by higher levels of nitric oxide and carbon monoxide. 
Compared to a control group, the daily supplementation of MSM at 8 mg/kg for five weeks protected these horses from oxidative stress and the exercise-induced inflammation that occurred from weekly competition over the study period. 
From these results it appears that MSM supports joint health by acting as an antioxidant and anti-inflammatory mediator.
Typically recommended serving sizes are 2 grams per 100 kg bodyweight. Some horses might benefit from a higher initial serving size of 20 grams per day until improvements are noted, followed by 10 grams per day on an ongoing basis.
THE VERDICT:Suitable evidence of efficacy in performance horses.