In early DJD, the only change may be a thickening of the synovial membrane and a thinner joint fluid. If the inflammation isnt arrested, this progresses to softening, grooving, and eventually thinning and erosion of the cartilage surface where it bears weight. As the joint cartilage wears and erodes, unhealthy fluid allows the bone edges to come in closer contact than normal. This can lead to irritation and osteophytes (or bone spurs, sharp, bony projections, seen here in this side view of a left front knee)

Degenerative joint disease (DJD) is probably the most common cause of performance-limiting lameness that threatens your trail horse, so it’s important to protect his joints from damage.

Here, we define DJD, explaining how it begins and progresses. Then we give you strategies to prevent DJD and tell you when it’s time to call your veterinarian. Plus, we give you two handy joint-supplement resource guides, one for manufacturers and one for retailers.

Joint Anatomy
To understand how joints break down, first you need to know a bit about joint anatomy. Here’s a rundown.

The equine joints most susceptible to breakdown are the fetlock, knee, elbow, hock, and stifle. hock, and stifle. These joints are heavily strained when your horse is moving. The bones that make up these joints are connected by strong ligaments (deep connective tissues) that begin above the joint and end on the bone below it. Ligaments bridge and stabilize the bones inside the joint.

The outermost layer of a joint is the joint capsule, a shell made from connective tissue that encloses the joint and holds the joint fluid (called the synovial fluid).

The next layer is the synovial membrane or synovium. The synovium is a double-layered membrane. The final layer facing the inside of the joint is very thin and secretes the synovial fluid. The tissues and membranes between the joint capsule and the inner layer of synovium vary from soft and fatty to very dense, depending on how hard the joint is worked.

Joint cartilage, also called articular cartilage or hyaline cartilage, is tough, pliable tissue that lines the ends of bones inside joints, protecting the joints from trauma. This tissue is a network of collagen (protein) fibers and ground substance, composed of water and the glycosaminoglycans (GAGs): chondroitin sulfate, hyaluronic acid (HA), and keratan sulfate.

Chondrocytes (specialized cells) sit inside lacunae (microscopic holes) in the cartilage, and secrete the collagen and ground substance. Cartilage has no nerve or blood supply. It gets its nutrition from the synovial fluid. When your horse moves, fluid in the lacunae is compressed out. As he takes weight off his leg, this fluid rushes back in.

Joint Breakdown
DJD (commonly called arthritis) is a process that involves the thinning and eventual erosion of cartilage. It’s essentially an imbalance between inflammatory processes that break down the cartilage and synovial fluid, and the ability of the chondrocytes to repair and replenish the ground substance.

When your horse exercises, there’s a normal release of "stress" factors called cytokines. At low levels, these can actually stimulate the cartilage cells and synovial lining to produce more GAGs. However, at high levels, cytokines trigger inflammation, which results in the release of destructive enzymes that can actually break down cartilage.

Joints can become inflamed due to uneven weight (or load) distribution. Uneven loads can be caused by conformational faults, obesity, unbalanced trimming and shoeing, and trail riding over uneven ground, where your horse’s hoof can’t land flat.

Note that the faster you ask your horse to go, the more force is applied to his joints. This increase in force increases his risk for inflammation and the development of DJD.

Another cause of joint inflammation is injury-induced trauma. A fall, a kick, and even a severe misstep can damage your horse’s ligaments, which can lead to long-term joint instability and eventually DJD.

Your horse’s age also comes into play. Young, growing horses are able to repair cartilage problems by producing new hyaline cartilage, but physically mature horses are not. The number of chondrocytes also decreases as your horse gets older, as does the amount of GAGs in the ground substance. Thus, the risk of developing DJD increases as your trail horse ages.

Joints can become inflamed due to uneven weight (or load) distribution. Uneven loads can be caused by conformational faults, obesity, unbalanced trimming and shoeing, and trail riding over uneven ground, where your horses hoof cant land flat.

Signs of DJD
In early DJD, the only change may be a thickening of the synovial membrane and a thinner joint fluid. If the inflammation isn’t arrested, this progresses to softening, grooving, and eventually thinning and erosion of the cartilage surface where it bears weight. Lameness may be mild, so inspect your horse’s joints daily for any signs of heat or swelling.

As the joint cartilage wears and erodes, unhealthy fluid allows the bone edges to come in closer contact than normal. This can lead to irritation and osteophytes (or bone spurs — sharp, bony projections).

As pain progresses, your horse may still not be obviously lame, but you’ll see such signs as tripping (due to a reluctance to normally flex his joints) and a shorter stride than normal. His gaits may feel uneven or stiff. You may notice he’s reluctant to pick up one lead, and/or balks when asked to go up or down hills. Or, he just may be grumpy and generally less enthusiastic about being ridden.

If your horse has DJD, he’ll likely feel stiff when you first ask him to work, then improve as he warms up. By the time he feels stiff or appears lame all the time, DJD has already reached an advanced stage.

Preventive Strategies
To help prevent DJD, take the following steps.

• Look for good conformation. If you’re currently in the market for a trail horse, find one with well-conformed joints, and good balance. Avoid a horse with feet that are small in proportion to his body; a trail horse’s feet are his shock absorbers. (If you need help evaluating good conformation and proportion, take along a reputable trainer or knowledgeable horseperson on your horse-hunting trips.)

• Exercise your horse regularly. Daily exercise is good for your horse’s joints. It stimulates the chondrocytes, and strengthens the joint capsules and ligaments. Good muscle tone stabilizes his large joints. If possible, keep your horse outside, where he has room to roam, play, and stretch.

• Maintain hoof balance. Work with your farrier to keep your horse’s hooves meticulously balanced. The hoof is your horse’s base of support. If that base is unbalanced, it negatively affects the entire leg, including the joints.

• Condition with care. Allow plenty of time when conditioning your trail horse. His muscles, heart, and lungs will respond to exercise much more quickly than his tendons, ligaments, and joints. He may seem to be handling his work load easily, but in reality, you may be asking too much of him. Work with your veterinarian to design a conditioning schedule appropriate for your horse.

• Ride sensibly. Use common sense when riding your horse over uneven terrain. Slow down, look ahead, and allow him to pick a safe path.

• Inspect his joints. Inspect and feel your horse’s joints daily. It doesn’t take long, and you’ll catch joint problems early — a good long-term investment in his health. (For signs of joint pain, see page 43.)

• Treat joint issues promptly. If your horse develops joint heat or pain, apply cold hosing or ice intensively to reduce inflammation. If the problem persists for longer than three days, call your veterinarian. (For more on veterinary treatments, see page 47.)

Joint Supplements
Over-the-counter joint supplements — also called nutraceuticals — are nutrients (natural substances) that are substituted for or used in conjunction with drugs/pharmaceuticals.

Although there’s relatively little scientific proof that joint supplements can prevent DJD, there’s considerably more to suggest they can at least slow it down. And they can help manage joint inflammation in lame horses.

Joint nutraceuticals come in several categories: the GAGs (as described in "Joint Anatomy"); avocado-soy unsaponifiables; cetylated fatty acids; manganese (a mineral); and plant/herbal preparations. Here’s a rundown of each category.

• Glycosaminoglycans. The GAGs include chondroitin sulfate, glucosamine sulfate or hydrochloride, acetylglucosamine (a metabolite of glucosamine), and HA. Glucosamine is actually the starting point in GAG synthesis. These are usually included as the purified substance, but natural sources, such as Pernal mussel or hydrolyzed collagen, are sometimes used. All have anti-inflammatory effects. Research has shown that the combination of glucosamine and chondroitin works better than either supplement alone.

• Avocado-soy unsaponifiables (ASU). ASUs are fatty acids tightly bound to fiber in avocado and soy and extracted in a laboratory. This formula has no anti-inflammatory effects, but may protect cartilage from breakdown.

• Cetylated fatty acids (Celadrin; cetyl-myristoleate). Cetyl-myristoleate was isolated from the cartilage of a strain of rats that’s resistant to developing arthritis. The first study on its use was successful in protecting rats, the next one was intermediate in effect, and the most recent found no protection at all. It’s never been studied in horses.

• Manganese. Manganese is commonly included in joint supplements, and is important in cartilage formation, but this mineral is very rarely deficient. Copper, zinc, and vitamin C are also important for joint health, but if your horse’s base diet is adequate, there’s no further advantage to adding more.

• Plant/herbal preparations. Plant and herbal pain-relieving, antioxidant/anti-inflammatory ingredients include yucca, devil’s claw, aloe vera, white willow, boswellia, MSM, bromelain, grapeseed extract, and resveratrol.

If you suspect your horse has degenerative joint disease, your vet will perform a lameness exam that consists of palpating (feeling) the joints, watching your horse move at a walk and trot, and flexion tests (shown). In flexion tests, your vet will hold the joint in question in a flexed position for 30 to 90 seconds, then will ask you or an assistant to trot your horse for observation.

Selecting a Supplement
Selecting a joint supplement among the hundreds on the market today can be a daunting task. To begin, look at the ingredients list. If your trail horse isn’t showing any particular symptoms, a glucosamine-chondroitin combination, with or without ASU, is a good choice.

If your horse’s joints are inflamed, you’ll likely achieve the most rapid results with an HA gel. Horses with chronic joint problems and stiffness that don’t respond to the usual combinations may benefit from a product that includes devil’s claw, or another ingredient for pain and inflammation. You might need to experiment to find the best product for your horse.

When you begin using a joint supplement, you might first notice that your horse is moving more freely overall. Changes are evident within days to weeks, although if you use HA to control pain and swelling, you’ll see a difference within a day or so.

If your horse is lame, improvements of a full lameness grade or more are possible. (For a description of lameness grades, see page 44.) If he has an advanced case of DJD, don’t expect him to become pain-free. But you may be able to greatly reduce or eliminate the need for prescription pain drugs, as well as injections performed by your veterinarian. (For more on veterinary treatments, see right.)

The only oral nutraceutical that has been tested in horses as a preventative is the newcomer, avocado-soy unsaponifiables. In an equine arthritis model, where arthritis was induced by surgically damaging knee cartilage, horses treated with ASU had much smaller lesions than untreated horses. Their pain and swelling wasn’t affected, but the cartilage was protected.

In another study, young horses that had surgery for osteochondrosis lesions were treated with oral HA gel (brand name Conquer, from Kinetic Technologies; www.kinetictech.net). They had significantly reduced postoperative pain, swelling, and lesion size compared to untreated horses.

Veterinary Treatments
Call your veterinarian any time your horse has joint inflammation that you’re not able to control within three days. Sudden, severe lameness also always warrants a vet call. Keep in mind, though, that DJD smolders more than it flames. If you even suspect than your horse may have DJD, call your vet, so he or she can start treatment.

Your vet will perform a lameness exam that consists of palpating (feeling) the joints, watching your horse move at a walk and trot, and flexion tests. In flexion tests, your vet will hold the joint in question in a flexed position for 30 to 90 seconds, then will ask you or an assistant to trot your horse for observation. The flexion will usually exaggerate any lameness problems.

If your vet finds a problem area, he or she will likely take X-rays. He or she might also use other diagnostic methods, such as ultrasound, a bone scan, or magnetic resonance imaging (MRI).

Your vet will then discuss treatment options with you. If your horse’s joint is actively inflamed, your vet may recommend a short course of nonsteroidal anti-inflammatory drug (NSAID). Oral NSAIDs include the familiar phenylbutazone (commonly called "bute"), flunixin meglumine (brand name Banamine), ketoprofen (brand name Ketofen), or compounded meclofenamic acid.

To minimize the side effects of gastric or colonic ulcers with these drugs, your vet may also prescribe firocoxib (brand name Equioxx, from Merial; www.equioxx.com).

Topical anti-inflammatories, which are applied to the skin around the joints, include DMSO and the NSAID cream SURPASS (from Idexx pharmaceuticals; www.idexx.com/equine).

Your vet may also recommend a series of joint injections, either systemic (injected into the bloodstream or muscle) or intra-articular (injected directly into the joint).

Systemic joint injections include the HA Legend (from Bayer HealthCare, Animal Health Division, www.bayerequineconnection.com), which is injected into the bloodstream, and polysulfated glycosaminoglucans (brand name Adequan i.m., from Luitpold Animal Health; www.luitpoldanimalhealth.com), which is injected into the muscle.

Intraarticular injections include corticosteroids (a class of medications related to cortisone that reduces inflammation) and injectable HA. Joint injections usually also incorporate a dose of antibiotic to guard against infection.

Among the new and still-experimental joint treatments are extracorporeal shock wave therapy (ESWT) and interleukin-1 receptor antagonist protein (IRAP) treatment. Here’s a bit about each one.

• ESWT. With this therapy, shock waves penetrate the joints, stimulating affected areas. The goal of ESWT is to decrease pain and possibly speed up joint fusion.

• IRAP. Interleukin-1 is an inflammatory cytokine that plays a key role in DJD. This treatment involves collecting blood into a special syringe that stimulates the platelets (small blood cells) to produce a protein that blocks interleukin-1. This is sent to a laboratory, which concentrates the protein and ships it back to your vet. Your horse will receive one to three injections. The interval between IRAP treatments is typically six months to a year. Vets using this procedure are reporting improved comfort in more than 75 percent of the horses treated.