Observations on the heart rate of thoroughbreds.

The study reports how heart rates change in 1,000 Thoroughbred racehorses after competition, identifying consistent three-phase recovery patterns and examining how age, race type, environmental conditions, and clinical variables influence post-race cardiac responses.

Study Population and Examination Conditions

• The author reviewed heart-rate records from 1,000 Thoroughbreds competing in 700 Flat races and 300 Hurdle/Steeplechase races across 54 British racecourses.
• Horses varied in age and fitness, with a wide range of race distances (5 furlongs to 4 miles) and conditions (“going” and weather).
• Heart rate measurements were taken using auscultation and radial pulse, with counting periods ranging from 20 seconds to over 1 minute.
• Most examinations occurred in looseboxes near the paddock under standard post-race cooling-out procedures (washing down, walking for ~10 minutes).
• Approximately 45% of horses examined were winners, and none were believed to be under the influence of prohibited substances.

Post-Race Heart Rate Patterns

• The study identifies a three-phase recovery period seen consistently across most horses:
  • Phase 1 (0–10 min): Heart rate remains elevated and relatively stable.
  • Phase 2 (10–20 min): A steep decline in heart rate occurs.
  • Phase 3 (20+ min): A gradual return to baseline that may take one to several hours.
• Flat racehorses typically had slightly higher post-race heart rates than National Hunt (Hurdle/Chase) horses, likely reflecting their younger average age and the nature of Flat racing.
• Limited longer-duration measurements suggested that older horses returned to resting heart rate faster than younger horses.
• Resting heart rates on the racecourse varied widely, from 44 bpm in a calm 7-year-old Chaser to 96 bpm in an excitable 3-year-old colt.

Heart Rate Values: Early Post-Race

• At 3–5 minutes after stopping:
  • Flat racers averaged 114 bpm.
  • Hurdlers/Chasers averaged 106 bpm.
• Over 90% of horses had heart rates between 91 and 130 bpm during this early window.
• Average heart rates continued to fall between 10 and 60 minutes post-race, with National Hunt horses generally showing slightly lower values at each interval.

Extreme Fast and Slow Post-Race Heart Rates

• High heart rates:
  • 5.5% of Flat horses exceeded 130 bpm shortly after pulling up.
  • Six horses exceeded 140 bpm; five showed signs of respiratory disease or fever, and one had a marked arrhythmia.
  • Only 7 of 300 National Hunt horses exceeded 130 bpm, one due to severe injury.
• Low heart rates:
  • 1.2% of Flat horses recorded < 90 bpm post-race.
  • 7% of Hurdlers/Chasers showed slow post-race heart rates, particularly in long-distance (2–3½ mile) events.

Influence of External Factors

• During the first post-race minutes, external stimuli had minimal influence on heart rate.
• During later recovery phases, stimuli such as:
  • the sound of a galloping horse,
  • public address announcements,
  • movement back into the paddock

  could raise heart rate by 30% or more.

• By this stage, most horses appeared more “settled,” and 70% urinated during the later recovery period.

Heart Sounds and Cardiac Irregularities

• Auscultation immediately after racing was often difficult due to excitement and synchronized breathing/heartbeat frequencies.
• In most horses only the first and third heart sounds were clearly audible.
• The fourth heart sound was distinctly audible in 3% of horses shortly after racing, rising slightly at 30–40 minutes.
• The third heart sound was extremely rare (0.3%), appearing transiently in two horses and replacing the fourth sound in one.
• Fewer than 1% of horses showed cardiac defects considered serious enough to require further investigation.

Respiratory Rate Relationships

• Respiratory rates shortly after a race varied widely (30–120 breaths per minute), averaging around 70.
• No consistent relationship between heart and respiratory rates was observed.
• Occasionally, respiratory rate exceeded heart rate for brief periods post-race.
• Race distance, climatic conditions, footing (“going”), and horse fitness influenced both cardiovascular and respiratory recovery.

Overall Interpretation

• The study provides one of the earliest large-scale datasets describing how equine athletes recover physiologically after racing.
• The identification of a structured, predictable three-phase pattern offers a framework for understanding normal and abnormal recovery profiles.
• Findings suggest that:
  • age and discipline influence recovery kinetics,
  • environmental factors can meaningfully disrupt later recovery phases,
  • most cardiac irregularities identified were minor or clinically insignificant.
• The study remains relevant to modern assessments of racehorse fitness, welfare, and post-exercise monitoring.