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

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.