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

Abstract

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 (P = 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 (P < 0.05) at 24 h post-SET, independent of treatment. Horses receiving HA exhibited reduced (P = 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.

Keywords: biomechanics; exercise; horse; hyaluronic acid; range of motion.

Figure 1.

Physiological parameters of the standardized exercise test. Horses receiving a placebo (CONTROL, n = 8) or HA injection (n = 8) were exercised on a motorized treadmill. Blood was collected for plasma lactate concentration before and at the indicated time after exercise (A). Heart rate (HR) was recorded throughout the exercise test and maximal HR in beats per minute (HRmax, bpm) was extracted (B). The time to reach 50% of HRmax was extracted from the data (C) as a measure of recovery time. Means and SEMs are shown. No treatment differences were noted for any physical or biochemical parameter.

Figure 2.

Fetlock flexion in adult horses following a standardized exercise test (SET). Horses received an IV injection of saline (CONTROL, n = 8) or HA (n = 8) prior to and after a SET. Flexion through the left and right metacarpophalangeal joint was measured and values were averaged. Means and SEMs are shown.

Figure 3.

Hindlimb hock flexion, extension, and range of motion in adult horses following an exercise test. Horses received an IV injection of saline (CONTROL, n = 8) or HA (n = 8) prior to and after a standardized exercise test. Horses were trotted in hand across a flat surface and evaluated by high-speed videography. Change in flexion (A, B) and extension (C, D) was calculated as maximal angle minus angle at stance. Range of motion (ROM) was calculated as the sum of flexion and extension for right (E) and left (F) hock. Means and SEMs are shown.