Promoting Lifelong Equine Joint Health
By Nancy S. Loving, DVM • Jul 23, 2016 • Article #29798
Photo: Anne M. Eberhardt/The Horse
Horse owners are painfully aware that the predominant factor limiting a horse's athletic longevity is musculoskeletal injury--particularly joint problems. A common assumption is that these injuries result from wear-and-tear and age. Consequently, owners further assume there's not much to be done about it. But think again: Using sensible strategies we can promote healthy equine joints capable of withstanding athletic demands.
Nutrition From the Start
The journey to long-term joint health starts with the initial decision to breed a specific mare to a stallion. Earl Gaughan, DVM, Dipl. ACVS, previously a clinical professor of large animal surgery at the Virginia-Maryland Regional College of Veterinary Medicine and now a technical services veterinarian at Merck Animal Health, says, "Selection of both stallion and mare for strong conformational attributes may improve known structural deficits in either individual." He also recommends researching siblings' and offspring's history to better understand a potential cross outcome. "(The parents') performance history is relevant as well," says Gaughan. "Despite many notable imperfections in structure, many equine athletes perform successfully."
From conception to foaling, broodmare nutrition affects the fetus' joint health and might impact his chances of having developmental orthopedic disease (DOD, musculoskeletal problems) as a youngster. A mare's feed intake and mineral ratios (zinc, copper, calcium, phosphorus) contribute to proper cartilage maturation, particularly in the last trimester. Because mare's milk is a poor source of trace minerals, a foal depends on his liver mineral stores, such as copper, for several months after birth. Copper helps mineralize (strengthen) the cartilage matrix and aids bone development. While a foal's liver store of copper does not reduce DOD incidence, it does help improve and repair lesions that arise.
"Foal growth does not occur on a smooth continuum or a steady, progressive increase in size but is, rather, a 'ratcheted' affair that includes growth spurts," explains Gaughan. "Close observation along with management of a foal's caloric intake are important strategies to avoid fueling the fire of rapid or excessive growth (which contributes to DOD development)."
The lactating mare's diet impacts her foal's caloric intake: Excessive feed intake results in abundant, rich milk, prompting foal growth spurts. Thus, practitioners consider this excessive feed intake in the mare to be a bigger contributor to musculoskeletal issues than inadequate feed, and researchers have linked excess calories and energy intake to DOD lesion development in young horses.
A foal's caloric intake is also a more important consideration than protein concentration in his diet. Researchers have not associated any musculoskeletal problem with high dietary levels of protein in published studies; in fact, adequate protein (14-16% of the foal's total diet) is important for proper bone development. Scientists have linked diets containing less than 12% protein with reduced growth rates and poor cartilage mineralization. Most importantly, excessive energy (calories) can fuel excessive growth and subsequent abnormalities associated with improper endochondral (within cartilage) ossification of joint cartilage, in which soft cartilage cells transform into hard bone cells.
As with the gestating mare's ration, mineral balance (particularly calcium-phosphorus and copper-zinc ratios) in the growing foal's diet is critical to proper musculoskeletal development. "Many commercial feeds intended to support the growing foal have appropriate balances of minerals and essential components to achieve the objective of steady growth," says Gaughan.
Exercise management is crucial for the rapidly growing horse and is best coupled with a balanced feed ration. "Articular cartilage manages its nutrition and waste product production via normal use and weight bearing," says Gaughan. "Exercise is good but in excess could lead to -problems."
Avoiding excessive exercise strain helps reduce potential injuries in foals that could result in growth plate trauma or subchondral (under the cartilage) bone cyst formation within joints. "Moderate exercise with gradual increases in intensity and duration results in better cartilage health and fewer injuries than that imposed by sudden, high-intensity loading," stresses Gaughan.
However, it is equally important not to limit a growing youngster's exercise too much since strain-force application (from loading the limbs) helps bone and soft tissue develop properly. David Frisbie, DVM, PhD, Dipl. ACVS, ACVSMR, of Colorado State University's Equine Orthopaedic Research Center, reports, "We have seen more joint injury in horses not worked until they are 2 years old compared to foals that receive some controlled exercise."
Common sense dictates carefully controlled voluntary exercise such as paddock turnout; for a young horse in training find a middle ground. "Loading that occurs with normal weight bearing and light turnout exercise may be all that is required for acceptable cartilage development," emphasizes Gaughan. Trainers commonly use longeing and round pen work when starting youngsters. However, "human-controlled exercise should be delayed until a young horse can be restrained effectively," says Gaughan. "Waiting until at least the yearling stage to start longe line work seems appropriate, and it's best to wait even longer if folks can be patient.
"There's evidence that articular cartilage responds in a 'handed' fashion--if a young horse works in one direction more than another, cartilage development can differ between limbs," he adds. "The objective should be to familiarize the young horse with the longe line or round pen rather than attempting conditioning-training work. Implement early exercise in a thoughtful, deliberate manner that limits excessive repetition, which is challenging not only to joints but to tendon, ligament, and muscle as well."
Gaughan stresses that exercise management becomes particularly important when early signs of DOD become evident, such as joint and limb swelling, slight or overt lameness, limb angle deviation from normal, and/or limb flexural deformity. These signs indicate the owner should control, reduce, or halt exercise and consult a veterinarian promptly.
Preventing injury is the primary objective in long-term joint health management in horses of all ages. For the grown horse in training, Frisbie advises, "Good body weight and muscle strength are the most important goals, along with conditioning for the specific exercise demands the horse will be performing."
When a joint injury does occur, the owner plays an essential role in rapid detection. "Close observation and knowing a horse's structure and personality are helpful," says Gaughan. "Seek veterinary attention at the first notice of abnormal clinical signs, such as swelling, heat, pain, and/or lameness; joint effusion (excess fluid in a joint space) is typically the first abnormal sign seen after joint injury. With time and progression, a steady decline in performance associated with gait changes or a horse's reluctance to perform expected athletic efforts should be key concerns as well."
Ultimately, the earlier an owner and veterinarian recognize and treat a joint insult the better the result. "Continued exercise on even mildly injured tissue can create a long and frustrating course of disease progression and treatment," says Gaughan. "Working through it is rarely a good idea."
Instead, he advises stopping exercise, contacting your veterinarian for evaluation, and applying cold water and/or ice immediately after signs of joint injury. It's best to withhold non-steroidal anti-inflammatory (NSAIDs, such as phenylbutazone and flunixin meglumine) administration until speaking with your veterinarian, he says. These drugs are invaluable for decreasing inflammation, but their ability to mask pain could complicate exam findings.
To improve the horse's athletic outcome, Gaughan recommends, "Accurate assessment of joint injury is essential to develop an appropriate treatment plan. A thorough physical and lameness examination by your veterinarian helps narrow the concerns to a specific joint(s). Additional diagnostic tools further define the injury: diagnostic nerve blocks, joint fluid assessment, radiography, ultrasonography, nuclear scintigraphy, and MRI."
He emphasizes that the primary goal is to restore joint anatomy and function--including joint fluid--to normal. "This protects the synovial membrane (which lines the joint and secretes joint fluid) and joint cartilage to re-establish function as quickly as possible," he explains.
Systemic (intravenous [IV] or intramuscular [IM]) treatments as well as corticosteroid and hyaluronic acid (HA) injection directly into an injured joint have been effective in controlling the joint injury's inflammatory cascade. "Intra-articular (IA) and systemic administration of hyaluronan and PSGAGs (polysulfated glycosaminoglycans) is associated with reduction in cellular and chemical mediators of inflammation," explains Gaughan. Frisbie considers these moderators of inflammation, along with the IA corticosteroid triamcinolone, to be chondroprotective (protecting the cartilage).
Many horse owners wish to tackle joint health proactively using joint supplements--a popular and common trend in the horse world. "Investigative work strongly supports the ability of systemic (in this case, non-oral) and intra-articular agents containing hyaluronan and PSGAGs to reduce inflammation and protect cartilage against degradation, particularly in injured and inflamed joints," says Gaughan. "Extrapolation from studies infers that these agents potentially protect normal joints from athletic stresses and may reduce the severity of injury by supplementing naturally occurring similar substances. This has led to prophylactic (preventive) use of IV and IM joint supplements, such as Legend (HA), Adequan (polysulfated glycosaminoglycans), and Pentosan (pentosan polysulfate)."
Frisbie notes, however, that none of these medications are labeled or approved for prophylactic use yet.
Gaughan says, "For a drug administered through a needle (subcutaneous [in or under the skin], IM, IV, or IA) to be labeled for such use, Food and Drug Administration requirements must be met through exhaustive, verifiable research work." However, he cautions, "The same cannot be said regarding products for many oral nutraceuticals, such as those containing glucosamine or chondroitin sulfate--the FDA has no role in quality assurance or proof of claims for nutraceuticals."
Studies on various oral products have revealed that not all contain a therapeutic concentration of specific ingredients. For example, scientists have proven an oral unsaponified avocado and soy supplement benefits joint health when dosed at 6 grams daily, says Frisbie. However, it's unknown whether commercial products containing half this amount will provide sufficient therapy. While joint-related feed supplements likely cause little harm, a horse might receive less-than-expected benefits at an expense to the owner.
Advanced methods of managing joint health to maintain a horse's athletic longevity include biologic therapy, also referred to as regenerative therapy, such as IRAP (interleukin-receptor antagonist protein) or stem cells. "None of these current therapies are regenerative in the true sense of the word," Frisbie explains. "However, in numerous cases they've been shown to increase the health of joint tissues over more traditional methods."
To produce IRAP for joint injection, "blood (taken directly from the horse to be treated) is activated on glass beads, incubated, centrifuged, and stored in syringes," Gaughan explains. "This IRAP solution blockades interleukin and other major mediators of joint inflammation; it also contains numerous growth factors to reduce inflammation and pain while encouraging tissue healing."
Stem cells are harvested from two potential sources: adipose tissue or bone marrow. "Stem cells, specifically those expanded from bone marrow culture, have demonstrated improved cartilage repair over standard surgical techniques alone," says Frisbie. "Early promising results have been achieved for stifle meniscal lesions in returning horses to work by combining surgery and stem cell therapy as compared to surgery alone. A study at Colorado State University followed horses for over two years and revealed a significantly better clinical outcome from stem cell use." Frisbie advocates that the best stem cell results come from bone marrow-derived products when administered at least 30 days after injury rather than rushing treatment within the first few weeks.
"Additional value may be achieved with (extracorporeal) shock wave therapy, particularly to address soft tissue structures of an injured joint," Frisbie adds. "Underwater treadmills have also provided good benefits for rehabilitation of an injured joint."
Throughout a horse's life, from conception through advanced athletics, opportunities exist for horse owners to manage joints for the best musculoskeletal outcome. Proactive strategies begin before conception by selecting an appropriate mare and stallion. From gestation through growth and development, balanced nutrition and sensible exercise programs impact joint cartilage health. Careful, strategic conditioning programs promote progressive strengthening of musculoskeletal tissues. Recognizing lameness early, obtaining an accurate diagnosis, and selecting appropriate therapies are critical to returning a horse's joint to optimal function and keeping him in fine athletic fettle for the long-term.