The effects of bovine somatotropin (bST) and porcine somatotropin (pST) on growth factor and metabolic variables in horses.

The study investigates the impact of bovine and porcine growth hormones (bST and pST respectively) on metabolic and growth factors in horses. The study suggests that these hormones are biologically active in horses and result in similar metabolic responses as seen in other mammals.

Study Design

The research involved three different studies performed on lighthorse mares weighing between 455 to 545 kg.

• The first study involved eight mares that received five subcutaneous injections of either bST or pST (30 mg/d).
• In the second and third studies, a different set of five mares each received a single subcutaneous injection of a prolonged-release formulation intended to deliver 500 mg of either bST or pST over a 14-day period.

In all cases, blood samples were regularly obtained before, during, and after treatment to establish baseline values and evaluate the effects of the hormones.

Results

Within 48 hours after administration of either bST or pST, the researchers observed a decrease in blood urea nitrogen concentration and an increase in insulin-like growth factor I (IGF-I) concentrations.

• Similarly, levels of insulin and glucose also increased relative to pretreatment values following bST or pST administration.
• In the case of the second and third studies which involved the prolonged-release formulation, circulating somatotropin (ST) concentrations were found to be increased for at least 14 days post-injection even though severe local tissue reactions were noted at the injection site.

Conclusion

This study affirms that bST and pST are indeed biologically active in horses. These hormones produce metabolic responses similar to those seen in other mammals. Additionally, the results pointed out the presence of circulating insulin-like growth factor binding proteins in horses.

However, the commercially available dairy cow product POSILAC was found to be unsuitable for delivery of bST in horses due to local tissue reactions following the administration of the oil-based prolonged-release formulation.