Diurnal rhythm and effects of feeding, exercise and recombinant equine growth hormone on serum insulin concentrations in the horse.

The research paper investigates the impact of feeding, exercise, and equine growth hormone therapy on the insulin levels in healthy horses. The study reveals that equine growth hormone therapy increases insulin levels, which is not rectified by exercise, making the treatment unsuitable for managing obesity in insulin-resistant horses.

Objective and Methodology

• The primary aim of the study was to examine how feeding, physical activity, and equine growth hormone therapy influences the basal insulin concentrations in horses.
• The study involved an in-vivo experimental study with 12 geldings, from whom blood samples were collected every half an hour over a 24-hour period. This was done to determine their baseline serum insulin concentrations before initiating them on a 3-week exercise programme.
• Post this period, the horses were categorized into two groups and engaged in further exercise for another 4 weeks.
• Group A was treated with daily intramuscular injections of equine growth hormone. The dosage was structured to start at 5 mg/day for the first five days, before increasing to 12.5 mg/day for the remaining 16 days.
• Blood samples were collected before feeding each day to measure serum insulin levels.

Results and Conclusions

• Horses showed insulin spikes within two hours of feeding and the insulin levels were much lower between midnight and 07:30 h.
• The study revealed that the exercise did not affect basal insulin concentrations prior to the administration of equine growth hormone.
• However, equine growth hormone injections resulted in a significant increase in serum insulin concentrations in Group A as compared to their initial levels.
• The study also found that this hormone therapy induced variable hyperinsulinaemia in the treated horses, which decreased in intensity once the administration of the hormone stopped.
• Based on the research findings, the study concludes that, to measure basal insulin concentrations, single serum samples should be taken prior to the morning meal.
• Equine growth hormone therapy increased the basal insulin concentrations in horses, an effect that was not counterbalanced by physical exercise.
• Given the induced hyperinsulinaemia and based on the observed results, the researchers do not recommend using equine growth hormone therapy to manage obesity in insulin-resistant horses.