The effects of ostarine on clinical health parameters in adult horses

Selective androgen receptor modulators, such as ostarine (also called enobosarm), are androgen receptor ligands that initiate tissue-selective activation of androgenic signaling and have demonstrated potential in enhancing muscle mass and physical performance with minimal androgenic side effects in humans. Due to its anabolic effects, ostarine is used for illegal doping in horses, presenting a problem for ethical horse racing, and possibly also for horse safety and health. There are currently no studies that investigated the effects of ostarine on equine health. Thus, the goal of this study was to investigate whether ostarine adversely effects the clinical health of horses. We hypothesized that ostarine would alter indicators of heart health, but no other clinical health parameters investigated in this study. A total of 9 idle adult horses (mean age ± SD = 17.2 ± 2.5 years) were enrolled, 4 of which received intravenous (IV) injections of 62 mg ostarine in 1 mL ethanol 4 times a week (on nonconsecutive days) for 4 weeks, while the remaining 5 horses received 1 mL of ethanol (IV) at the same times to serve as controls. The treatment duration was based on a rodent study. Clinical exams were performed by the same experienced person once before injections, weekly during the injection period, and at 2 weeks and 4 weeks postinjection. Data were analyzed descriptively and using a mixed model ANOVA with treatment group, exam day, and their interaction fitted as fixed effects. Ostarine-treated horses did not have significantly different respiratory rates (P = 0.76), rectal temperatures (P = 0.65), or heart rates (P = 0.37), compared with the control group at any of the recording time points. Abnormal heart sounds were only recorded once during the study in a control horse. No signs of depression or abnormal lung sounds were recorded in any of the horses throughout the study. Abdominal sounds were present, but abnormal abdominal sounds were not recorded in any of the horses during the study. These findings suggest that ostarine administration, at the dose, administration frequency and route used in this study, does not significantly alter the basic clinical health parameters investigated. While ostarine might thus be considered safe to use in idle adult horses under these conditions, there is still little understanding of its potential long-term effects, the effects on other clinical and nonclinical health parameters, as well as the effects in exercising horses. In addition, this study was of small sample size, and it is thus possible that it was not powerful enough to detect smaller, but meaningful, differences between the treatment and control groups.