Though circular exercise is a common practice across many disciplines during both ridden and non-ridden exercise, it may be at the detriment of the bone and joint health of horses. In this study, 42 sheep were striated by sex and weight then randomly assigned to treatment groups determining various exercise protocols. Exercise was conducted on either a straight line, small circle (12 m diameter) or large circle (18 m diameter) at either a slow (1.3 m/s) or fast (2.0 m/s) speed. This study also utilized a non-exercised control. Sheep were exercised 4 d/wk for 12 wk. At the end of the study, all animals were humanely euthanized. Synovial fluid was collected from the carpus. All joints of the carpus and metacarpophalangeal joint were opened, photographed, and lesions were assessed. Cartilage samples were collected from the proximal surface of the fused third and fourth metacarpal. All forelimbs were collected for computed tomography scan analysis and biomechanical testing. Statistical analysis was performed in SAS 9.4. A total of 411 lesions were found, though there was no significant effect of treatment or leg. Bone mineral density was found to be lower in the lateral and medial cortices of the left leg of sheep in the large slow treatment group (p < 0.05). Fracture force tended to be higher in the right leg of sheep in the large, fast treatment group (p = 0.08). Serum osteocalcin and crosslinked c-telopeptides of type-I collagen were both found to have day (p < 0.05) and treatment (p < 0.05) effects. No effects of treatment or leg were found regarding markers of cartilage or synovial fluid quality. These results indicate that circular exercise may influence bone and joint health and that sheep are a valuable model species for musculoskeletal research.
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