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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)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To compare exercise-induced immune modulation in young and older horses.

Animals

6 young and 6 aged horses that were vaccinated against equine influenza virus.

Procedure

Venous blood samples were collected for immunologic assessment before and immediately after exercise at targeted heart rates and after exercise for determination of plasma lactate and cortisol concentrations. Mononuclear cells were assayed for lymphoproliferative responses and incubated with interieukin-2 (IL-2) to induce lymphokine-activated killer (LAK) cells. Antibodies to equine influenza virus were measured.

Results

Older horses had significantly lower proliferative responses to mitogens than younger horses prior to exercise. Exercise caused a significant decrease in lymphoproliferative response of younger horses, but not of older horses. Activity of LAK cells increased slightly with exercise intensity in younger horses. Cortisol concentrations increased in both groups after exercise; younger horses had higher concentrations after exercise at heart rates of 180 and 200 beats/min than those of older horses. Plasma lactate concentrations increased with exercise intensity but there were no differences between older and younger horses. Older horses had lower antibody titers to equine influenza virus than younger horses. Exercise did not affect antibody titers.

Conclusion

Although lymphoproliferative responses and antibody titers of older horses were less than those of younger horses, older horses were more resistant to exercise-induced changes in immune function, possibly because of lower cortisol concentrations.

Clinical Relevance

Stress and aging are known to affect immune function. Older horses had reduced immune function, but were more resistant to exercise-induced immune suppression than younger horses. (Am J Vet Res 1999;60:643–647)

Free access
in American Journal of Veterinary Research