Making Equine Bones Stronger

This paper is a clear explanation of factors that predispose to injuries in sport horses and how to prevent them.
DrO

Animals (Basel) 2023 Feb 22;13(5):789.
A Review of Three Decades of Research Dedicated to Making Equine Bones Stronger: Implications for Horses and Humans
Brian D Nielsen 1

Abstract
Much research has been conducted in an attempt to decrease skeletal injuries in athletic horses. The objective of this literature review is to compile the findings of over three decades of research in this area, make practical recommendations, and describe how research can develop over the years. An initial study investigating the role of bioavailable silicon in the diets of horses in race training produced the unexpected finding of decreased bone mineral content of the third metacarpus subsequent to the onset of training. Further studies revealed this decrease to be associated with stall housing eliminating high-speed exercise, leading to disuse osteopenia. Only relatively short sprints (between 50 and 82 m) were necessary to maintain bone strength and as few as one sprint per week provided the needed stimuli. Endurance exercise without speed fails to elicit the same benefits to bone. Proper nutrition is also required for optimal bone health, but without the right exercise, strong bone cannot be maintained. Several pharmaceuticals may have unintended consequences capable of impairing bone health. Many of the factors influencing bone health in horses also exist in humans including a sedentary lifestyle, improper nutrition, and pharmaceutical side-effects.

Conclusions
Many without research experience believe solutions to problems can often be achieved through a single study. By contrast, this paper highlights how it can sometimes take decades, utilizing dozens of studies, to be able to make solid, research-based recommendations. Often a single study will inspire other studies to answer new questions that arise. Additionally, sometimes research provides incidental findings that may prove to be more important than are the findings for which the study was designed.

While originally looking for a nutritional approach to preventing skeletal injuries, a loss of bone mass of the third metacarpal of horses in race training was shown. Trying to find ways to prevent that bone loss led to the realization that the loss was due to stalling of horses without access to speed. Future studies showed that pasture turnout prevented that bone loss and as little as one short sprint per week made dramatic differences in bone strength. Failure to provide athletic horses with such an opportunity would seemingly put them at increased risk of injury—particularly once high-speed work resumes.

Exploring whether stalling of horses caused the loss of bone mass was inspired by a mentor who had no horse experience and, thus, was not biased by how things have traditionally been done in the horse industry. Currently, many in the horse industry believe that training of young, growing horses is detrimental and should not be done. However, scientists working in this area realize that is not the case [56]. Bone modeling, the process by which changes in the size, shape, and strength of bone occur, happens primarily in the juvenile animal. Once skeletally mature, changes primarily occur through bone remodeling—the process which involves simply replacing old or damaged bone. Thus, little change in size, shape, and strength can occur once skeletal maturation is complete.

Nutrition does play an important role in bone health. Having the necessary nutrients in proper balance is crucial to bone development, particularly in the growing horse [57]. However, examining studies using markers of bone metabolism to detect treatment differences, those studies involving changes in nutrition usually failed to show differences, whereas studies involving altering exercise usually resulted in significant differences in those biochemical markers [58]. Likewise, in young female humans, only childhood physical activity had a significant positive on bone density, as opposed to nutritional and other lifestyle factors that had no influence [59]. Granted, this is based upon the assumption of adequate Ca intake and other nutrients, and this is especially true after menopause [60]. These studies emphasize the benefit of an active lifestyle on the skeletal system, particularly when young and growing to achieve a higher peak bone mass upon maturity. However, activity is still crucial when older as a sedentary lifestyle hastens bone loss and is permissive to osteoporosis, regardless of diet. These findings do not lessen the importance of proper nutrition on bone health, it simply suggests that once requirements are met, providing additional nutrients cannot assure good bone health. It also suggests it is not possible to have optimal bone health if no exercise, or the wrong type of exercise, is provided, regardless of what is consumed through the diet. While the temptation by some is to fault nutrition for skeletal injuries, more often it is improper training, management, or lifestyle that is to blame.

Research also suggests caution be taken when providing pharmaceuticals that may inhibit mineral absorption or enhance mineral loss, though proper exercise and nutrition may mitigate potential negative effects. More concerning are pharmaceuticals that inhibit normal bone metabolism, such as by reducing osteoclastic activity, as this can impair normal bone healing [53]. Additionally, potential analgesic effects should be of great concern whether with pharmaceuticals such as bisphosphonates or corticosteroids [61]. Masking pain when an injury is still present increases the chance for greater injury, potentially even catastrophic in nature, to occur.

Though the intent of much of the afore-mentioned research was to improve the lives, health, and well-being of horses, implications also exist for humans. A sedentary lifestyle, without sufficient mechanical loading of bone, will lead to a weakened skeleton. With the lifespan of humans being longer than horses, failure to strengthen the skeleton when young, and failure to maintain skeletal strength when mature, likely will increase the risk of skeletal injury throughout life and increase the chance of developing osteoporosis when older. Improper nutrition will increase the risk, though proper nutrition, without the correct form of exercise, will not prevent it. Fortunately, as with horses, the proper exercise does not require long bouts of exercise. Short bouts (only about 20 cycles) of bone-centric exercise can increase bone strength without the damage that repeated cycles can cause [62]. Again, like with horses, having a skeleton adapted for high load requires loading while young, continuing through maturity. Attempts to improve skeletal health once mature is more difficult to accomplish and much greater care needs to be given to managing loads placed upon it and preventing bone loss when aging.

With both horses and humans, many of the skeletal injuries that develop are the result of bone being ill-prepared for high loads due to sedentary periods without loading. As quoted by Dr. Gary D. Potter, the author’s major professor in graduate school at Texas A&M University, when an old horse trainer was asked what he believed to be the major cause of injuries in his racehorses, his answer was respiratory problems. The trainer claimed he did not know why, but it seemed like every time one of his horses became sick and needed to be rested for a while, it became injured when he put it back in training. With decades of research to support it, the answer is clear.