Take a proactive approach using your horse’s diet

Let me guess: You read the title of this article and assumed it was just another piece about joint supplements. Surprise, it’s not! Rather, this discussion about joint health will center around how certain nutrients support these structures and their development.

But first things first: What makes up a healthy joint? Every joint comprises two bone ends covered by articular cartilage and encased within a joint capsule, a thin, saclike structure. The capsule’s inner layer, called the synovial lining, secretes synovial fluid that prevents friction between the joint structures. The outside layer of the capsule is fibrous, and that, along with the surrounding collateral ligament, helps stabilize the joint. The articular cartilage contains a matrix of collagen, proteoglycans, and water. -Proteoglycans are molecules that help organize connective tissue so that it is elastic, yet strong, and are made up of chains of glycosaminoglycans. These are a type of carbohydrate, attached to a protein, that give cartilage its stiff structure. Synovial fluid contains two key ingredients that give it its lubricating qualities: hyaluronic acid, another glycosaminoglycan type that’s also present in cartilage, and a protein known as lubricin.

Proper nutrition can literally make or break joint health. Although a foal’s diet as it grows influences skeletal health most, its nutrition throughout adulthood also plays a role. We typically think of minerals such as calcium and phosphorus when talking about bone integrity, but vitamins, amino acids (the building blocks of protein), and energy also have their place when feeding for joint health. Let’s dive into joints and what a horse’s nutrition should look like over its life.

Young, Growing Horses

Do you have a big-boned Hanoverian filly that’s growing like a weed? Then pay attention. Postnatal growth is our main window to potentially optimize the horse’s long-term skeletal health. Growing horses are at risk of acquiring developmental orthopedic diseases (DODs). These encompass all growth disorders in foals, including osteochondrosis (OC, which causes lesions in the cartilage and bone of youngsters’ joints—not to be confused with osteochondritis dissecans, a loose bone fragment), subchondral cystic lesions, angular limb deformities, physitis (growth plate inflammation), flexural deformities, cuboidal bone abnormalities, and juvenile osteoarthritis. Factors that predispose foals to DODs include bone trauma, rapid growth rates, genetics, hormonal imbalances, and, not surprisingly, nutrition.

Surveys by German and Dutch researchers indicate OC can affect all horse and pony breeds and its incidence in horses younger than 2 might be as high as 50%. Diet prior to and throughout weaning is key to proper joint cartilage maturation; OC results when the cartilage matures abnormally.

Feeding that Thoroughbred colt to sell him as big, strappingly handsome yearling, for instance, might have dangerous consequences. That’s because feeding excess energy (calories), which leads to greater weight gain and growth, might negatively affect his skeletal development, especially if other nutrient needs (such as protein) are not met.

Researchers in Australia found that when they fed energy at 120% of National Research Council’s (NRC, authors of Nutrient Requirements of Horses) recommendations per day, weanling foals developed OC lesions consistently, while their counterparts fed energy at 100% daily didn’t. Researchers have implicated energy from concentrates, in particular, as a cause of OC lesions due to the connection between certain hormones and cartilage development. The hormone insulin affects articular cartilage growth, and post-meal elevated blood glucose and subsequent insulin levels might alter the cartilage growth.

In a 1996 study researchers at Rutgers University fed a diet of 50% commercial sweet feed and 50% alfalfa grass mix hay to eight weanlings, four yearlings, and three 2-year-olds, four of which had radiographic (X ray) evidence of OC lesions. The scientists observed higher post-meal changes in blood ­glucose and insulin ­levels in youngsters with OC lesions, implicating a connection between metabolism and joint ­development.

Contrary to popular belief, feeding high or low levels of protein impacts foal growth rate but not DOD development. In pigs, feeding high levels of certain amino acids reduced the severity and number of OC lesions, although researchers have not evaluated whether this happens in horses.

Calcium and phosphorus contribute the most to bone and joints’ mineral pool. A reversed calcium-to-phosphorus ratio (less than one to one) and calcium or phosphorus deficits, regardless of the ratio, can negatively affect a young, growing horse’s joints, says Sarah Ralston, VMD, PhD, Dipl. ACVN, who recently retired from her post as professor and associate director of teaching at Rutgers University, in New Brunswick, New Jersey.

The microminerals copper and zinc help the horse’s body develop and repair collagen. In a study of Thoroughbred mares grazing on pasture with low dietary copper (less than 10 parts per million), for instance, copper supplementation significantly reduced the incidence of physitis in their foals.

Excessive vitamin A (>100,000 International Units per day to an average sized pregnant mare) has been implicated as a cause of birth defects in horses, which can occur if a pregnant mare consumes multiple supplements and fortified grain, says Ralston.

So what can we do to optimize joint health in young, growing horses? NRC authors say joints appear to have different “windows of susceptibility” after which OC lesions are less likely to resolve on their own—at about five months of age for hocks and eight to 12 months for stifles.

“The goal should be to provide adequate energy, protein, and mineral intakes to sustain a steady growth rate throughout the first year of life to avoid DODs,” says Ralston.

Around the second or third month of age, the calcium and phosphorus levels in the mare’s milk might no longer meet the growing foal’s needs. At this point owners often supplement the foal’s diet with creep feed or minerals designed for growth, particularly if the forage does not adequately meet their needs, either.

After weaning Ralston suggests feeding the best-quality forage available, such as a legume mix for quality protein and mineral intake. Feed at least 2% of the horse’s body weight per day in dry forage matter. If concentrates are needed to balance minerals, Ralston recommends using forage-based products designed specifically for rapidly growing young horses. If feeding a grain-based product, feed no more than 0.25% to 0.4% body weight per meal, and do not exceed 1% body weight per day. When using a highly concentrated supplement such as a ration balancer, which is designed to be fed in very limited amounts, be sure to follow feeding recommendations on the label.

Broodmares

In 1938 researchers at the University of Cambridge, in England, began to unravel the connection between maternal environment and nutrition on foal development. They found that newborn Shire-Shetland Pony crossbred foals were proportional in weight to their dams and almost the same weight as purebred foals of the maternal breed—that is, the crosses out of Shire mares were comparable in birthweight to the pure Shire foals. In fact, the crosses out of Shire mares were three times larger than the crosses out of Shetland mares. This indicates just how influential nutrition can be for development. During pregnancy the mare’s daily nutrition requirements are high enough to maintain her own condition, as well as support the growing fetus. Most fetal growth occurs during the third trimester, and nutritional needs change accordingly.

According to Nutrient Requirements of Horses: Sixth Revised Edition (2007), the mare’s calcium and phosphorus requirements increase around the seventh month of pregnancy as the fetus begins to use these minerals. While she’s lactating, her calcium and phosphorus needs remain elevated. Mares mobilize calcium from their own bones during this time, but bone mineral density returns to normal once they’re no longer producing milk.

Calcium and phosphorus deficiencies can have dramatic consequences in developing foals, such as enlarged joints and poor bone mineralization. In 1993 Michael Glade, PhD, found that foals from mares on diets containing insufficient calcium levels had weaker bones at birth. Because mare milk contains very little copper and foals are not capable of absorbing copper well during the first few months of life, maternal copper intake vitally influences the foal’s copper stores in the liver during gestation. Elevated copper in the liver at birth appears to help repair cartilage lesions (van Weeren et al., 2003). A mare’s inadequate copper intake might result in her foal developing OC lesions; however, in a large study of Hanoverian foals, researchers reported no relationship between mare copper intake and foal OC lesions (Winkelsett et al., 2005). Clearly, more work needs to be done to understand the connection between dietary copper and DODs.

The overall composition of the mare’s diet might also affect her foal’s long-term skeletal integrity. Mares fed concentrates during gestation were more likely to produce foals affected by DODs than mares fed all-forage diets (Vander Heyden et al., 2013). In a 2017 study out of Austria, researchers compared the effects of feeding mares a diet of forage, or of forage and cracked barley, from mid-gestation through foaling on post-weaning growth. Maternal undernutrition with the forage-only diet resulted in foals born with narrower cannon bones. When the foals were 20-24 months of age, the researchers fed them 140% of their total daily nutrient requirements. While the scientists did not note any growth rate differences, they did find that foals from mares fed the cracked barley diet had metabolic differences, suggesting that maternal diet has a “fetal programming” effect during gestation.

Mature Horses

Joint trauma happens daily as part of a performance horse’s normal wear and tear, commonly leading to inflammation of the synovial membrane (aka synovium) and joint capsule. This can result in excessive synovial fluid production, called effusion, that can cause pain and reduced performance. Over time, the articular cartilage matrix might start to degrade, eventually progressing into degenerative joint disease or osteoarthritis (OA, the degeneration and loss of articular cartilage within a joint). Osteoarthritis is one of the most common causes of lameness and poor performance in horses, says Annette McCoy, DVM, MS, PhD, Dipl. ACVS, assistant professor of equine surgery at the University of Illinois College of Veterinary Medicine, in Urbana.

Joint trauma, extended confinement, poor conformation, improper shoeing, and age are the primary contributing factors to OA development, she says, with trauma, either as a single or repeated events, as the main initiating factor.

“Trauma, in this case, may reflect supraphysiologic (abnormal) forces on normal tissue or physiologic (normal) forces on abnormal tissue, and does not have to directly affect the articular cartilage,” says McCoy.

The joint is, in fact, an organ that consists of many tissues, and injury to any one of them can lead to OA. For example, says McCoy, there is good evidence that inflammation starting in the synovium or the joint capsule as a whole can initiate a catabolic cascade that eventually results in cartilage destruction, even if there was no initial structural damage to the cartilage. “Unfortunately, a major challenge in managing OA is that by the time clinical signs (i.e., lameness) occur, irreversible cartilage damage has already occurred,” she says.

Little can be done to improve joint health through diet once the horse is older than one year. Oral joint supplements and injections might help prevent or delay joint issues, but little can be done nutritionally other than to provide a balanced diet that meets daily requirements.

Take-Home Message

In a study of U.K. horses, researchers found that mineral intakes, particularly of calcium and phosphorus, were significantly higher than current recommended daily amounts (Grimwood et al., 2015). Similarly, in a U.S. survey of elite show jumpers’ diets, scientists found they were consuming inadequate phosphorus, yet they were getting almost two times the amount of calcium necessary to meet requirements (Pratt, 2016). Feeding commercial grain mixes and a variety of supplements can easily result in an unbalanced diet. Make sure to evaluate your horse’s total diet, especially if you own a young horse or broodmare, to maximize skeletal health and development for a lifetime of healthy joints.