Swimming exercise and race performance in Thoroughbred racehorses

Swimming-has become an accepted part of the training programme of race horses. The purpose of this study was to establish whether it was passible to perform a standardized swimming test in race horses and to evaluate whether exercise variables calculated from this test were related to race track performance. Fifty-two Thoroughbred racehorses (4.6 +/- 1.4 years; 50 geldings and 2 stallions) participating in races at the Hong Kong Jockey Club (HKJC), were used in the study. All horses underwent a swimming test consisting of two laps of an oval shaped swimming pool (1 lap = +/- 60 m). During the swimming test, heart rate (HR; beats/min) and speed (V; m/s) of the horses were monitored. Additionally, 10 of the 52 horses were tested a second time (after 1-21 days), to evaluate the repeatability of the swimming test and after the second swimming test plasma lactate concentration (LA; mmol/L) was estimated. 'Performance Rating' of horses was defined by the rating score determined by the HKJC, based upon race performance. For a second performance parameter ('Performance Category'), horses were divided into 'good performers' (placed in 1 to 5 rank at competition in the period between 1 month before to 1 month after the swimming test) and 'average performers' (placed at lower rankings). Mean HR during the first swimming test was 178 +/- 14 bpm, the mean V was 1.06 +/- 0.10 m/s. There was a significant correlation between HR and V (r = 0.720, P < 0.001, n = 52), but HR was not repeatable between tests (r = 0.390, P = 0.265, n = 10). No significant correlation was found between racing performance and heart rate, speed or plasma lactate concentration. Under the existing circumstances it was not possible to perform a repeatable standardised swimming test. The results of the swimming test were not a useful predictor of either Performance Rating or Performance Category. Some horses reached high heart rates during the swimming test and one horse also showed a plasma lactate concentration above anaerobic threshold, indicating that the exercise of swimming may not be always as mild as some trainers think.