Brian D. Nielsen, from Michigan State University's Department of Animal Science, conducted an extensive review of over three decades of research focused on improving skeletal strength in athletic horses, particularly racehorses. These horses often face significant stress on their leg bones from a young age. This research not only highlights the evolution of studies in equine health but also offers scientifically-backed strategies to reduce injuries in horses—insights that might also apply to human athletes.
The Impact of Dietary Silicon
The research began by exploring whether supplementing horses with a bioavailable form of silicon (Si) could reduce injury rates. In a study involving 53 Quarter Horses in training, the benefits of sodium aluminosilicate (SZA), a source of Si, were evident. Horses given low, medium, and high doses of the supplement had fewer injuries and were more likely to complete the race program compared to those in the control group. It was observed that horses in the medium and high dosage groups covered more distance in training before encountering any injuries, suggesting that silicon supplementation might enhance their resilience to the demands of racing.
Further studies explored potential reasons for this reduced injury rate, including research on yearlings and postpartum broodmares. These studies hinted at a possible connection between altered bone turnover and injury reduction, potentially allowing for faster bone repair. Concerns about aluminium content in SZA led to the evaluation of oligomeric orthosilicic acid (OSA) as an alternative Si source without aluminium. Additionally, a marine mineral supplement was tested, showing promising results in increasing bone turnover in yearling horses.
However, when retired Standardbred racehorses were given a bioavailable Si supplement to examine its effect on lameness, the results were less conclusive. The study questioned whether Si supplementation provided any benefit to older horses or if the commercial dosage was sufficient to elicit a response.
Bone Loss Due to Stall Housing
An unexpected discovery in the initial study was the decrease in bone mineral content (RBAE) after 62 days of training. This bone loss persisted until the study's conclusion, with the most significant injuries occurring between days 60 and 120—coinciding with the period of lowest bone mass. The young horses had been moved from pasture to stalls before training began, which limited their access to free exercise. This confinement likely contributed to the loss of bone mass, as the skeletal system received less loading stress.
To investigate this further, 16 Arabian yearlings were divided into two groups: one remained on pasture, while the other was confined to stalls with one hour of daily walking on a mechanical walker. After 28 days, the RBAE of the stall-confined horses had decreased, and this trend continued throughout the 140-day study. Even when the horses began race training, no increase in bone mass was observed. This study highlighted the detrimental effects of stall confinement on bone health, raising concerns about the common practice of stalling young racehorses during early training.
Another study compared bone mineral content in mature Arabian horses that were conditioned but then confined to stalls for 12 weeks. Despite daily walking and a high-calcium diet, these horses also experienced bone loss. This suggests that even partially confining horses can lead to significant decreases in bone mass, highlighting the importance of pasture access in maintaining skeletal health.
The Role of Speed in Bone Strength
Research into the effects of speed on bone health revealed that not all exercise is equally beneficial. A study with 18 weanlings showed that short sprints significantly increased bone mineral content and altered bone geometry, compared to horses confined to stalls without sprinting. This finding underscores the importance of mechanical strain in bone development, as bone responds more to the intensity of bending than the frequency.
Another study challenged the belief that slow, steady training strengthens bones. Eleven two-year-old Arabians were split into two groups: one underwent high-speed treadmill training followed by regular endurance exercises, while the other group lived on pasture without forced exercise. After 162 days, no significant differences in bone mineral content were found between the two groups, suggesting that endurance exercise alone may not enhance bone strength as much as free-choice exercise on pasture.
Pharmaceutical Considerations
Caution is advised when administering pharmaceuticals that may impact mineral absorption or increase mineral loss, such as bisphosphonates or corticosteroids. Bisphosphonates, approved for treating navicular disease in horses over four years old, inhibit bone resorption, raising concerns about impaired bone healing, particularly in young horses.
Furosemide, commonly used in racehorses to prevent pulmonary haemorrhage, was studied for its impact on calcium balance. While it was found to temporarily disrupt calcium levels, the effects were short-lived, returning to baseline within three days. Similarly, omeprazole, used to treat gastric ulcers, did not appear to inhibit calcium absorption at preventative doses, though longer use or higher doses might pose risks.
The initial study on bioavailable silicon unexpectedly revealed that bone mineral content decreases after the onset of race training, largely due to stall confinement and lack of high-speed exercise. However, even short sprints can maintain bone strength, while endurance exercise alone does not provide the same benefits. Proper nutrition is crucial for bone health, but it must be paired with appropriate exercise to be effective. Additionally, some pharmaceuticals may have unintended consequences on bone health, warranting careful consideration.
Many of the factors that influence bone health in horses, such as a sedentary lifestyle, improper nutrition, and pharmaceutical side effects, are also relevant to human athletes.