Endocrinologic, hematologic, and heart rate changes in swimming horses

Area of Science:

• Equine physiology and sports medicine

Background:

• Understanding the physiological responses of horses to exercise is crucial for training and performance.
• Swimming is an increasingly utilized exercise modality for equine athletes, necessitating detailed physiological evaluation.

Purpose of the Study:

• To investigate the acute effects of a swimming regimen on heart rate, hematologic parameters, and key hormones in Standardbred and Thoroughbred horses.
• To determine how swimming duration and time of sampling influence these physiological variables.

Main Methods:

• Two identical experiments were conducted on Standardbred (n=31) and Thoroughbred (n=17) horses using a standardized swimming protocol.
• Horses were categorized by swimming duration (1-5, >5-10, >10-15, >15 minutes).
• Heart rate, packed cell volume (PCV), plasma total protein, cortisol, triiodothyronine, thyroxine, insulin, and glucose were measured pre-swim, immediately post-swim, and 1 hour post-swim.

Main Results:

• Significant effects of sampling time were noted for PCV, total protein, triiodothyronine, thyroxine, and insulin in Experiment A.
• Swimming duration significantly affected insulin concentration, and interactions between duration and sampling time influenced heart rate and cortisol in Experiment A.
• Experiment B showed significant effects of sampling time on all measured variables except glucose.

Conclusions:

• Swimming induces short-term physiological changes in horses, affecting hematologic and endocrine markers.
• The duration of swimming and the timing of sample collection are critical factors influencing these physiological responses.
• These findings provide valuable insights into the acute effects of swimming exercise on equine physiology.