Page 1357 - Veterinary Immunology, 10th Edition

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FIG. 40.10 Although a moderate amount of exercise is good for
the immune system, excessive exercise causes severe stress that
can be immunosuppressive. In this example, six thoroughbred
horses were subjected to a treadmill-based exercise challenge of
various intensities (speed and incline). Blood samples were
assayed for plasma cortisol levels by radioimmunoassay, and
influenza virus–specific lymphocyte proliferation was assayed by
thymidine incorporation. A clear relationship exists among exercise
intensity, the stress response, and immune responsiveness. (From
data provided by Drs. S.G. Kamerling, P.A. Melrose, D.D. French, and D.W.
Horohov.)

The complex effects of extreme exercise on the immune system
are well seen in dogs undergoing long endurance sled races. The
proportion of dogs with low total globulin immediately after racing

was significantly greater than before racing. In some of these dogs it
remained low 4 months after the race. IgG was also lower after
racing than before racing. Likewise, serum IgM and IgE were
higher before racing, although IgA was higher after racing. These

changes in immunoglobulins might well affect resistance to
infectious diseases. There is also evidence of increased
inflammation in these dogs after racing.
Transportation stress is well recognized as predisposing to the

development of respiratory disease in horses and cattle. Prolonged

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