The effect of recombinant equine growth hormone on the biomechanical properties of healing superficial digital flexor tendons in horses

Abstract

Objective: To evaluate the effect of recombinant equine growth hormone (rEGH) on the in vitro biomechanical properties of healing superficial digital flexor tendon (SDFT) in horses.

Study design: Completely randomized design.

Sample population: Twelve Standardbred horses, 3 to 7 years of age, with ultrasonographically normal forelimb SDFT.

Methods: One week after induction of collagenase (2,000 U) induced superficial flexor tendonitis, horses were randomly divided into groups of 6. One group was administered intramuscular rEGH (10 microg/kg/day for 1 week, then 20 microg/kg/day for 5 weeks), whereas the other group (control subjects) were administered an equivalent volume of saline (0.9% NaCl) solution. At the end of this 6-week treatment, horses were killed and one forelimb SDFT from each horse was harvested for biomechanical testing under uniaxial tension. Results were analyzed using an unpaired Student's t test; significance was set at P <or=.05.

Results: SDFT from horses treated with rEGH had significantly larger mean cross-sectional areas and lower mean values for ultimate and yield tensile stress, whereas tendons from the control group were biomechanically stiffer than those from the rEGH-treated horses.

Conclusions: Administration of rEGH to horses for 6 weeks, 1 week after collagenase induced injury to the SDFT, resulted in a significant increase in tendon cross-sectional area, a concomitant reduction in ultimate and yield tensile stress, and reduced tendon stiffness.

Clinical relevance: Using this model of tendonitis, rEGH had a negative effect on the biomechanical properties of equine SDFT in the early phases of healing. Based on our results, administration of rEGH to treat superficial flexor tendonitis cannot be recommended.