Effect of conditioning horses with short intervals at high speed on biochemical variables in blood

There is limited published work on the effect of training using intensive and short intervals of exercise to condition horses for racing.

To examine the effect of conditioning horses 1, 2 or 3 x a week using 2 short fast exercise intervals on blood lactate (LA), plasma ammonia (NH3) and urea (urea) as well as creatine kinase (CK) activity.

Thoroughbreds (age 4-5 years) were conditioned at near maximal speed (12-14 m/sec) over 100 m, on 2 occasions separated by a 10 min period at walk, on dirt track (conditioning exercise; CE) during a 6 week conditioning period (CP). The CE was undertaken either once (5 horses), twice (5 horses) or 3 times a week (4 horses) during a CP. Before, every 2 weeks during and after the CP, blood was drawn during the CE at 0, 2 and 4 min after each run and additionally 6 min after the 2nd run to measure blood LA and determine the maximal LA post exercise (LAmax). Plasma NH3 was measured in the same samples and the maximal NH3 post exercise (NH3max) determined. Additional blood samples were taken from the horses when stabled before the CE, and 12 and 24 h after to measure urea and CK activity in plasma.

There was no differential effect of the number of weekly CE on LAmax, NH3max, LA and NH3 immediately after exercise (LAO and NH3O). Conditioning did not have an effect on LAmax and LA0 after the 1st interval (P>0.05), but LA0 after the 2nd interval was lower after conditioning. NH3max after the 1st and 2nd exercise interval decreased in response to the conditioning, but not NH3 immediately after exercise (P>0.05). Median plasma CK activity 12 h after exercise was higher than before exercise and returned to preexercise levels 24 h post exercise when horses were exercised once and twice/week. In contrast, the median plasma CK activity of horses exercising 3 times/week remained at the pre-exercise level 12 and 24 h post exercise (P>0.05).

Conditioning horses with 2 intervals of 100 m at near maximal speed had a positive effect on blood LA and plasma NH3.

With the type of exercise examined, the fitness of racing horses can be maintained and eventually improved. In further studies the effect of increasing the number of runs in one exercise session should be investigated.