Factors influencing resting heart rate in endurance racehorses

In endurance racing, horses are stopped several times during a race for a veterinary inspection at so-called vet gates and heart rate is the relevant factor for the decision to continue the race. The influence on resting heart rate (HRResting) of endurance racehorses of the following factors was examined: 1) variation by day; 2) morning and afternoon variation; 3) ambient temperature and relative humidity; 4) age and v 4 (v 4 = speed at which the blood lactate concentration is 4 mmol/L under the defined conditions); 5) the method used to determine HRResting: auscultation or heartrate meter (HRM). Methods: The HRResting of 19 horses conditioned for endurance racing was determined. They were exercised either in a field or on a treadmill. It was found that HRResting: 1) differed between days (P < 0.001 in the treadmill group, P = 0.047 in the field group); 2) was higher in the afternoon than in the morning in the field group only (P = 0.001); 3) increased with higher ambient temperature (P = 0.024) while relative humidity did not affect it; 4) was not related to the age or v 4 of the horses; 5) measured by HRM was higher than by auscultation (P = 0.001). In conclusion the determination of HRResting of a horse should be based on a mean value determined after measurements taken on several consecutive days under as far as possible standardised conditions.