Joint Stresses in the Performance Horse
By Pam Harrison BSc (Hons) Physiology, Consultant to TRM, manufacturer of the Stride range of Natural Mobility Supplements for Performance Horses.

In all working horses, the skeletal structure is constantly absorbing shock and cartilage within the joints, which functions as a ‘shock absorber’, is particularly subject to significant, repetitive stresses. With increasing workload, so the frequency and often intensity of the stress increases.

As a result, the horse’s ability to maintain healthy cartilage in all its joints is absolutely fundamental to soundness, which for trainers and competitors necessitates an understanding of the factors pre-disposing the horse to injury, along with management regimes aimed at maintaining cartilage and hence joint health.

Ground conditions, nutritional status, fitness and fatigue all play a role and being aware of joint health is now an important aspect of training and competing horses successfully, especially at the higher levels of modern equestrian sport. Other factors include trauma, age, the locomotory demands of the difference disciplines and a genetic predisposition to disease.

Cartilage in the joints, correctly described as articular cartilage, is resilient within the horse’s normal physiological limitations, but an overload of work can begin the process of cartilage breakdown. An overload of just 5% is sufficient to initiate what is commonly known as Degenerative Joint Disease (DJD).

DJD is a common problem in competition horses, most frequently affecting the hocks, knees, front fetlocks and front navicular bones and can end careers. The health of articular cartilage depends on a delicate balance between the formation and the degradation of its components.

Articular cartilage can be thought of as ‘the last defence’ for a horse’s joints and comprises four layers of cells, covering the ends of bones forming joints and bathed by synovial fluid (joint fluid) contained within the joint capsule. Damage is quantified by how many layers of cartilage are affected by erosion and how large an area is affected. Seriously damaged areas, if replaced by bony tissue from the base of the cartilage layer, will result in the joint losing its compressibility, manifesting as reducing joint function in a progressively lame horse. The stage and development of disease will affect the efficacy of treatments and the outcome, but if there is early diagnosis, it is now known that the body can regenerate cartilage tissue, dependent on the availability of essential nutrients.

To help prevent damage happening in the first place, the same nutrients necessary for joint repair must be available in the amounts required, or the cartilage will lose its ability to replenish and repair itself. As cartilage has no direct blood supply, it must receive nutrition via the synovial fluid, hence the importance of also maintaining the integrity of the synovial fluid. A good joint supplement will provide all of the required nutrients, helping to reduce inflammation, improving the synovial fluid and the cartilage.

The three most discussed nutrients required to replenish the cartilage matrix occur naturally in the body, hence can be called nutraceuticals and supplementation has been shown as beneficial in the maintenance of healthy cartilage.

These three nutraceuticals are glucosamine, chondroitin sulphate and methylsulfonylmethane (MSM) and together can support the healing process in the cartilage matrix. Some researchers have indicated they may also have a prophylactic effect on joints.

It is beyond the scope of this article to discuss the detailed physiology of these processes, but in somewhat simplistic terms, glucosamine and chondroitin sulphate act synergistically to stimulate the synthesis of new cartilage, whilst simultaneously inhibiting the activity of degradative cartilage enzymes. This helps to normalise the cartilage matrix, in essence treating DJD at the cellular level.

MSM is a source of bio-available sulphur, which is known to play a critical role in the synthesis of connective tissue (including cartilage) so when there is a joint problem, the amount of sulphur available should be increased in order to support tissue repair.

In addition MSM is useful within a management programme to help ease pain and increase mobility in the joint, at the same time facilitating sustained cell ‘flow-through’, allowing harmful substances to flow out and at the same time permitting nutrients to flow in. This can speed up the timescale for delivery of nutritional support to a compromised joint.

Synovial fluid not only acts as the ‘carrier’ pathway for the exchange of nutrients and waste products between the general circulation and the specialist cells responsible for cartilage regeneration, it also provides lubrication for the joint, a function provided by the hyaluronate fraction of the fluid.

As a result, again somewhat simplistically, it follows that hyaluronate (commonly known as hyaluronic acid or HA) is essential for the correct function of the synovial fluid and hence the joint, with changes in its composition now regarded as sensitive indicators of the degree of inflammation caused by a joint injury. It has been shown by researchers that increasing levels of HA in damaged joints can be beneficial by improving the quality of the synovial fluid, leading to improved joint function, so supplementing with HA is also recognised as offering potentially significant benefits.

The first clinical trials investigating the effectiveness of glucosamine took place in 1969 and since then, the scientific evidence supporting the value of high quality joint supplements has increased irrefutably. What is equally evident from reading some of the landmark research is that the formulation of a product and the levels of inclusion of its key ‘actives’ – glucosamine, chondroitin, MSM and hylauronic acid (HA) - will impact on the extent to which it can positively influence the health and integrity of stressed or diseased equine joints. Everyone with responsibility for performance horses will encounter joint problems at some point and understanding the importance of correct nutrition to long term soundness makes sound common sense.

This article has been kindly provided TRM Ireland, manufacturers of Stride, Stride HA and Stride MP. For further information or advice, please visit their website www.trm-ireland.com, email info@trm-ireland.com, telephone +353-45-434258 or write to TRM Ltd. Industrial Estate. Newbridge. Co. Kildare. Ireland.