Determining the effect of ostarine on senior horse clinical health

Abstract

Population estimates suggest that every sixth senior horse is affected by low muscle mass. Currently, there are no approved drugs that target muscle atrophy in horses. Ostarine is a selective androgen receptor modulator that has been found to promote muscle hypertrophy in humans. Ostarine could be a candidate drug for muscle atrophy treatment in horses; however, it is currently unclear whether ostarine is safe to use. Thus, the aim of this study was to determine whether ostarine adversely affects senior horse health. We hypothesized that ostarine would alter indicators of cardiac health, but no other clinical health parameters examined in this study. Four geldings (mean age ± SD = 24.3 ± 1.9 years) received 30 mg ostarine in 1 mL of 100% ethanol intravenously (IV) while the control group (n = 4 geldings, mean age ± SD = 22.8 ± 1.6 years) received 1 mL of 100% ethanol IV. There were 4 weeks of daily injections. Clinical data were recorded by the same experienced person 3 times before the injection phase, weekly during the injection phase, and weekly post injections for 3 weeks. Data were analyzed descriptively and using a mixed model ANOVA with treatment group, day, and their interaction used as fixed effects. There was no significant main effect of group on heart rate (P = 0.47), nor a significant day by group interaction effect (P = 0.47). For respiratory rate, there was no significant main effect of group (P = 0.13), but a significant group by day interaction effect (P = 0.001). A post hoc Tukey test showed that the control group had a significantly higher respiratory rate than the treatment group 2 weeks after the last injection (P = 0.02). For rectal temperature, there was no significant main effect of group (P = 0.71), nor a group by day interaction effect (P = 0.91). None of the horses exhibited signs of depression on any day. One horse in the control group presented repeatedly with abnormal heart sounds during the control, and the post control administration phases. There were no abnormal lung auscultations, nor abnormal gut sounds in any horse on any day, but normal gut sounds were present in all horses on all days. Based on these results, it can be concluded that ostarine does not seem to alter senior horse health overall, except for possibly reducing resting respiratory rate; although environmental factors could have contributed to the differences observed between the groups. Only a limited number of health parameters were investigated, and it is possible that this study was underpowered to detect smaller differences between the groups. Larger studies using a different drug dose, administration duration, and frequency may yield different results.