Effect of blood lactate-guided conditioning of horses with exercises of differing durations and intensities on heart rate and biochemical blood variables

The velocity at which blood lactate concentration ([LA]) of 4 mmol/L is reached ([v.sub.4]) is widely used to determine fitness, but there are few published data on using [LA] as a guide for the exercise speed for training in horses. In this study, the effect of 3 conditioning programs with [LA] guided exercise speeds on [V.sub.4], [V.sub.200] (speed at a heart rate of 200 beats/min), blood [LA], plasma FFA ([FFA]), and alanine concentrations ([alanine]), before and after exercise, as well as heart rate during exercise, of horses was examined. Six 2-yr-old Haflinger stallions underwent an initial treadmill-based standard exercise test (SET). A regression analysis [LA]-speed relationship was used to calculate [v.sub.1.5], [v.sub.2.5], and [v.sub.4]. Horses were then randomly assigned to 1 of 3 conditioning programs according to a 3 x 6 Latin square design. During 6 wk, horses exercised on the treadmill every other day for 45 min at their calculated [v.sub.1.5] or [v.sub.2.5] or 25 min at their [v.sub.4]. Each conditioning period (CDP) was followed by 5 wk without conditioning. At 2 and 9 d, and 5 wk, after the end of the CDP, the horses performed another SET to evaluate again the [v.sub.4] and [v.sub.200]. Blood [LA], plasma [FFA], and [ala nine] were measured before and after heart rate during exercise sessions 1, 11, and 21 in each CDP. None of the exercise programs had an effect on [v.sub.4] and [v.sub.200] (P > 0.05). The increase of the mean [LA] after exercise decreased during CDP (P < 0.05), and the increase of mean heart rate during exercise tended to decrease as well (P = 0.07). There was no difference among the conditioning programs. Plasma [FFA] before exercise was not influenced by the CDP (P > 0.05). The plasma [FFA] was always greater after exercise (P < 0.05), but there was no difference among conditioning programs. Overall, the increase was greatest after the 21st exercise session compared with the 1st and 11th exercise sessions (P < 0.05). The mean plasma [alanine] before exercise remained similar during all CDP (P > 0.05). Mean plasma [alanine] of the horses was increased after all exercise sessions measured (P < 0.05). There was no difference among conditioning programs (P > 0.05). It is concluded that conditioning with the exercise types used had small effects. This could have been because the exercise stress was too small, but also because the workload was not increased during the CDP. Key words: alanine, blood, conditioning, exercise, horse, lactate