Changes in heart rate, heart rate variability, and atrioventricular block during withholding of food in Thoroughbreds.

The research article concerns a study on how withholding food from Thoroughbred horses impacts their autonomic nervous system balance, as indicated by changes in their heart rate, heart rate variability, and frequency of second-degree atrioventricular block.

Research Methods

• The research experiment was conducted on five healthy Thoroughbred horses.
• It involved two 24-hour periods where, in one cycle, horses were fed normally (control group), and in the other, food was withheld.
• During these periods, the horses were kept in their stalls and their heart functions were monitored using ECG recordings from a Holter monitor.
• The ECG readings were then analyzed using a technique called fast-Fourier transformation.
• The research also took into account the low-frequency and high-frequency variations in the horses’ heart rate.
• Blood samples were taken at predetermined times to measure cortisol, ACTH, norepinephrine, and glucose concentrations in the plasma.

Research Findings

• Findings showed that withholding food resulted in a notable decrease in heart rate (HR) and an increased frequency of second-degree atrioventricular block, a type of heart arrhythmia.
• The circadian rhythms of the heart rate remained similar whether food was withheld or not; peak HR was observed between 7:00 pm to 8:00 pm, while the lowest HR occurred in the early morning.
• The research also revealed significant increases in the low-frequency and high-frequency components of heart rate variability during periods when food was withheld.
• Additionally, the cortisol concentration in the horses’ blood was higher and the plasma glucose concentration lower at 6:00 pm during periods of food withholding.

Research Conclusions

• The researchers concluded that heart rate variability indicators can be responsive to changes in autonomic nervous activity. They suggest that these indicators could serve as clinical measures of the neuroendocrine response to stressors, like food deprivation, in horses.