Administration of sodium hyaluronate to adult horses prior to and immediately after exercise does not alter the range of motion in either the tarsus or metacarpophalangeal joints.

Hyaluronic acid (HA), a glycosaminoglycan found in joint synovial fluid, is administered to horses as an anti-inflammatory with lubrication properties. This experiment examined the effects of HA administered before and shortly after an exercise test on metacarpophalangeal (MCP; fetlock) and tibiotarsal (hock) joint range of motion (ROM). Horses were injected intravenously (IV) with placebo (4 mL, saline) or HA (4 mL, 40 mg) 24 h before performing a standardized exercise test (SET) on a high-speed treadmill and again at 6-h post-SET. Passive fetlock flexion was measured at 4 and 24 h post-SET. Hock flexion and extension were measured at 24 h post-SET by videography and kinematic evaluation at the trot. Parameters of the SET were sufficient to cause peak lactate values of 6.6 ± 0.15 mM and a maximum heart rate of 203.6 ± 4.8 bpm. A minor gain ( = 0.08) in fetlock flexion prior to SET was observed in HA horses that were not retained at either 4 or 24 h post-SET. Hock flexion in both limbs was greater ( < 0.05) at 24 h post-SET, independent of treatment. Horses receiving HA exhibited reduced ( = 0.04) right hock extension. No differences in either right or left hock ROM were observed between control and HA-treated horses. From these results, it is concluded that IV HA injections surrounding an exercise stressor offer no substantive gains in either fetlock or hock ROM.