Plasma beta-endorphin and adrenocorticotrophin in young horses in training.

The study investigates the effects of an intensive training program on the levels of plasma beta-endorphin and adrenocorticotrophin in young horses. It reveals that the hormonal response to exercise diminishes as the horses’ fitness increases, and the levels of these two elements decrease accordingly.

Research Methodology

• The researchers performed a controlled period of submaximal exercise on a treadmill on 6 young horses. This was done as a standardized stress test to observe the effects of intensive training on the animals.
• Circulating plasma concentrations of immunoreactive beta-endorphin (IR beta-EP) were measured before, during, and after the exercise period. This was performed to monitor changes in the hormone levels due to the training.
• The stress test was conducted on three different occasions over an intensive 14-week training program.

Findings and Conclusions

• Dramatic increases were observed in the plasma IR beta-EP in week 3 of the training program. These increases, however, were not replicated in the final exercise test during week 9, as no significant increase was observed in the plasma IR beta-EP concentrations.
• During the training period, the basal concentrations of plasma IR beta-EP significantly decreased.
• Plasma adrenocorticotrophin (ACTH) did not increase during exercise, although there was a trend of decreasing basal plasma ACTH towards the end of the training period.
• The fitness of the horses increased over the training period. As their fitness increased, their hormonal response to exercise diminished. This finding led the researchers to conclude that the standardised work test acted as a mild stress to unfit horses, but its effects decreased as the horses become fitter.

The study’s results highlight the adaptability of horses’ hormonal systems to physical stress and can have implications for the optimal design of exercise and training programs for professional and leisure horses.