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Published on: July 4, 2018
Overtrained horses alter their resting pulsatile growth hormone secretion
E de Graaf-Roelfsema1, P P Veldhuis, H A Keizer
1Dept. of Equine Sciences, Medicine Section, Faculty of Veterinary Medicine, Utrecht Univ., Yalelaan 114, 3584 CM Utrecht, The Netherlands. e.roelfsema@uu.nl
Summary
Intensified training in horses led to overtraining, altering nocturnal growth hormone (GH) secretion patterns. These changes, including increased GH peak number and altered half-life, suggest disrupted GH regulation and may serve as early overtraining markers.
Area of Science:
- Equine Sports Medicine
- Endocrinology
- Exercise Physiology
Background:
- Overtraining syndrome in athletic horses can negatively impact performance and health.
- Identifying early, reliable markers for overtraining is crucial for timely intervention.
- Nocturnal growth hormone (GH) secretion dynamics are sensitive to physiological stress.
Purpose of the Study:
- To investigate the influence of intensified and reduced training on nocturnal GH secretion and elimination in Standardbred geldings.
- To identify potential markers of early overtraining in horses based on GH dynamics.
- To assess the recovery potential after a period of reduced training.
Main Methods:
- Ten young Standardbred geldings underwent a 32-week training program with intensified training (IT) and control (C) groups.
- Blood samples were collected overnight (8 hours, every 5 minutes) at the end of training phases.
- GH secretory dynamics were analyzed using pulse detection, deconvolution, and approximate entropy (ApEn).
Main Results:
- Intensified training induced overtraining, evidenced by a 19% performance decrease compared to controls.
- Overtrained horses showed increased GH peak number (3.6 vs. 2.0), smaller peak secretion, prolonged GH half-life (15.2 vs. 7.3 min), and higher ApEn (0.89 vs. 0.49).
- Reduced training did not fully restore GH dynamics in overtrained horses.
Conclusions:
- Altered nocturnal GH pulsatility, characterized by increased irregularity, indicates a loss of coordinated GH regulation control in overtrained horses.
- Changes in GH secretion and elimination dynamics may serve as early indicators of overtraining syndrome in horses.
- The findings suggest that prolonged somatostatin withdrawal might underlie the observed disruptions in GH pulsatility.
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