Effects of recombinant equine growth hormone on in vitro biomechanical properties of the superficial digital flexor tendon of Standardbred yearlings in training.

This study investigates the impact of recombinant equine growth hormone (rEGH) on the biomechanical properties of the superficial digital flexor tendon (SDFT) in young, exercising Standardbred horses. The results indicate that rEGH, when administered at recommended levels, does not significantly enhance the in vitro biomechanical properties of the SDFT.

Study Design and Methodology

• The experiment used a randomized complete block design with twelve Standardbred yearlings.
• The horses underwent a 12-week training program on a high-speed treadmill, with a 10% positive incline.
• During this process, the test group of 6 horses received daily intramuscular (IM) injections of rEGH, while the control group received equivalent volumes of sterile water IM.
• The rEGH dosage was 10 microg/kg during week 4, followed by 20 microg/kg from weeks 5-9.
• Post 12 weeks, the horses were euthanized, and the left forelimb SDFTs were collected and stored at -70 degrees Celsius. A section of the mid-region of the SDFT was then tested under high tension until failure.

Variables and Testing

• Several biomechanical properties were assessed, including ultimate and yield tensile stress and strain, maximum load at yield and failure, tendon stiffness, and mode of failure.
• Data were analyzed with the use of an unpaired, two-tailed Student’s t-test. A statistical significance cut-off was set at P ≤ .05.

Results

• The study reported that yield and ultimate tensile stress were significantly lower in the rEGH-treated horses compared to the control group.
• A trend towards increased maximum displacement, higher ultimate tensile strain, and lower tendon stiffness were observed in the rEGH-treated horses compared to controls.
• There were statistically significant correlations found between tensile stress and cross-sectional area, as well as tensile stress and stiffness, both at yield and failure points.

Conclusion

• The study concluded that rEGH, administered at the manufacturer’s recommended dosage rates to maturing Standardbred horses in training, does not significantly enhance the in vitro biomechanical properties of the forelimb SDFT.
• From these findings, it can be inferred that the use of rEGH in young horses in training is unlikely to improve the physiological adaptation of the SDFT to exercise stress.