Swimming exercise and race performance in thoroughbred racehorses

Abstract

Swimming has become an accepted part of the training programme of race horses. The purpose of this study was to establish whether it was possible 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= ±60m). 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 ± 0.10m/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 standar-dised 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.