SUMMARY
Objective
To test the hypothesis that, compared with unfit young horses, unfit older horses have lower aerobic capacity and reduction in other indices of exercise capacity.
Animals
6 young (mean ± SEM, 5.3 ± 0.8 years and 445 ± 13 kg) and 6 aged (22.0 ± 0.4 years and 473 ± 18 kg) healthy Standardbred and Thoroughbred mares.
Procedures
The mares, accustomed to running on a treadmill, were tested by use of an incremental exercise test. None of the mares had received exercise training for at least 4 months prior to the study. During testing, mares ran up a fixed 6% grade, starting at a speed of 4 m/s, with 1 m/s increase every 60 seconds (omitting 5 m/s) until they reached fatigue. Maximal oxygen uptake (VO2max) was measured by use of an open-flow calorimeter. Venous blood samples (10 ml) were collected during the last 10 seconds of each step and were used to measure blood lactate concentration and PCV. Calculated performance indices included velocity at VO2max, maximal velocity, and velocity at lactate concentration of 4 mmol/L; work rate (watts) at those velocities also was determined.
Results
There were differences (P < 0.05) between old and young mares for maximal run velocity attained during the test (8.7 ± 0.5 versus 10.8 ± 0.5 m/s, respectively), VO2max (89.4 ± 4.3 versus 117.3 ± 9.5 ml/kg of body weight/min, respectively), and velocity at VO2max (8.0 ± 0.4 versus 9.8 ± 0.7 m/s, respectively). Also, velocity required to reach blood lactate concentration of 4 mmol/L was lower (P < 0.05) in old (7.5 ± 0.4 m/s), compared with young (10.2 ± 0.7 m/s), mares.
Conclusion
Older mares have substantially (−24%) lower maximal aerobic capacity than do young mares.
Clinical Relevance
Many horses participate in athletic activities into their late teens and some do so beyond the age of 20 years; thus, the need exists to explore ways to adjust training programs for older horses. (Am J Vet Res 1997;58:1468–1472)
