Do waiting times in endurance vet gates affect the cardiac recovery index?

The cardiac recovery index (CRI) is currently a key component of veterinary inspections to assess endurance horses metabolic status and fitness. Originally published by Ridgeway, it instructs veterinarians to subtract from the first heart rate (HR 1 ), collected when the horse is initially presented for examination, a second HR (HR 2 ), taken 1 min after the horse starts a 125 feet (38.1 m) out and back trot to assess gait. It is widely believed that an increase of more than 4 bpm from HR 1 might be an indicator of fatigue. The FEI rules instruct the veterinarians to start the stopwatch exactly 1 min after the HR 1 count instead of trot start, as described previously. The aims of this study were to investigate how time delays in the vet gate affect the HR 1 count and the CRI during endurance competitions, and to characterise and compare the time taken by veterinarians to measure the original version of the CRI (tCRI RIDG ) and the adapted CRI used in FEI endurance events (tCRI FEI ). Data from 972 veterinary inspections of horses that took place in different endurance competitions in three different venues were collected. There was no association between the time elapsed from entering the vet gate to the start of the HR 1 count or from the HR 1 count to the start of the trot-up and the HR 1 or the CRI (P>0.05). However, larger studies involving more venues and different layouts are needed to corroborate our findings and to characterise the sensitivity and specificity of the CRI regarding the baseline heart rate. Although this study did not show an influence of waiting times on the CRI, a reduced deviation from the mean observed across all veterinarians when using the original Ridgeway guidelines to calculate the CRI (tCRI RIDG ) seems to point a better time-wise consistency when this version is used.