Glucosamine is a popular nutritional supplement for horses that can treat osteoarthritis and problems with joint mobility as well as acting as a preventative measure.

Osteoarthritis (OA) is not just a disease that affects old horses. Available data shows that more than 60% of equine lameness is caused by OA, and it is widely accepted that OA can affect any horse at any age. In younger horses it may develop following an injury or trauma to the hardest-working joints in a horse’s body.

Equine joint anatomy
A joint is the point where two, or more, bones meet.

A horse’s joints are designed to absorb shock efficiently, allow smooth, comfortable movement, and effectively bear the weight of the horse’s body.

There are three types of joint: fibrous, cartilaginous, and synovial.

Fibrous joints are more or less immobile. They include joints in the skull and those between the shafts of some long bones.

Cartilaginous joints have limited movement. These are the joints of the pelvis and vertebrae as well as growth plates, which extend a bone’s length during the horse’s growing years.

Synovial joints are the most active joints in the horse’s body. They consist of two bone ends covered by a smooth, thin layer of resilient articular cartilage.

Synovial joints
The synovial joint is surrounded by a fibrous joint capsule which is attached to both bones and also the collateral ligaments which are located on either side of most joints. They are key components of the fetlock, knee, elbow, hock, and stifle joints and are the most likely to suffer trauma and wear and tear.

The joint capsule contains an inner layer called the synovial membrane. This lining secretes synovial fluid that lubricates the joint.

Synovial fluid
A key ingredient in synovial fluid is hyaluronic acid, also known as sodium hyaluronate or hyaluronan, which lubricates the synovial membrane. Glucosamine is a precursor, or building block, for hyaluronan.

Another substance in synovial fluid is a protein called lubricin which is the main lubricant of the cartilage.

Normal synovial fluid is colourless or pale yellow and clear.

Articular cartilage
Normal articular cartilage is made up of cells called chondrocytes which produce and regulate the much more abundant matrix.

The matrix is composed of a tough protein called collagen surrounded by proteoglycan.

Proteoglycan allows articular cartilage to hold a lot of water which is essential for it to do its work of allowing virtually frictionless movement between the bones.

Proteoglycan is composed of protein and glycosaminoglycans (GAGs). These GAGs are produced by the chondrocytes – and glucosamine hydrochloride is the building block of articular cartilage GAG.

It can be seen from this that glucosamine for horses is a building block for nearly all of the most important components of equine joints.

Equine joint disease and lameness
The synovial joints are the ones in a horse that are most prone to disease and problems. They are the hardest-working joints in the horse and suffer the most wear and tear.

A horse’s front legs bear 60-65% of the horse’s weight and so absorb more shock than the back legs when a horse is moving at speed. The knee, or carpal joint, is a very complex structure of three joints.

Joint disease and injury is the most common cause of lameness and, as previously stated, 60% of lameness is attributable to Osteoarthritis (OA).

In younger horses OA can come on after an injury – whilst in older horses it can be a result of wear and tear on the joints over many years.

Osteoarthritis
Osteoarthritis is a progressive and permanent deterioration of articular cartilage and its associated structures. As a result of OA, the synovial fluid produced will be of a poorer quality and so less effective at lubrication, and the synovial joint capsule will be disrupted.

There is a strong link between synovitis (inflammation of the synovial membrane), capsulitis (inflammation of the joint capsule) and cartilage degradation and any one of these conditions may start-up or worsen another.

The result of all this for the horse is a hot, swollen, inflamed and painful joint causing loss of mobility and probably lameness.

In a minority of cases radiographs and ultrasound scans may help a vet to diagnose a specific cause for the development of osteoarthritis. Arthroscopic surgery may also be a tool in providing a diagnosis and may offer therapeutic options.

Treatments for equine joint disease
Although OA is incurable, it can be managed. When a specific cause, or traumatic injury, can be found for the onset of joint disease, surgery can be an option to halt the joint degenerating further.

Where there is no specific cause, treatment is based around reducing the inflammation and the rate of degeneration.

Key aims are obviously to reduce pain and swelling and prolong the horse’s athletic function. Treatments include:

  1. Pain management via administration of non-steroidal anti-inflammatory drugs (NSAIDs) or corticosteroids
  2. Intra-articular medications (hyaluronic acid, polysulfated glycosaminoglycans)
  3. Intramuscular polysulfated glycosaminoglycans
  4. Weight management and dietary modification (adding omega-3 fatty acids)
  5. Non-weight-bearing exercises (e.g. swimming) and physical therapy
  6. Oral joint health supplements (OJHSs) including glucosamine for horses, chondroitin sulphate and MSM for horses (methylsulfonylmethane)

Pros and cons of various treatments
NSAIDs such as phenylbutazone (bute) are the most well-known and common treatments for pain and inflammation but prolonged use and high doses have been associated with side-effects involving the gastrointestinal tract and kidneys. Boswellia serrata, a herbal alternative to bute, is a powerful, natural anti-inflammatory and pain reliever.

Injecting anti-inflammatory corticosteroids intra-articularly is also an extremely common treatment method which can reduce inflammation but there are potential risks and complications and it is important to consult your vet for detailed advice on this option.

Polysulphated glycosaminoglycan has been shown to protect cartilage in a number of species and to produce clinical improvement after intra-articular or intramuscular injection. But, the principal GAG in these preparations is chondroitin sulphate (CS), which unfortunately is hard for the equine gastrointestinal tract to absorb because of the size of its molecules.

Equine joint supplements
Good quality supplements such as glucosamine, chondroitin sulphate and MSM are regarded as safe and free from side-effects and they are the most popular for horses.

Glucosamine is the building block of articular cartilage and studies of people who have taken glucosamine orally have shown improved physical performance and reduction of pain.

Glucosamine is recognised by the International League Against Rheumatism as a “symptomatic slow-acting” drug and has recently been recommended for the treatment of arthritis by a British National Health Service publication.