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Effects of Chronic Heat and Cold Stressors on Plasma Immunoglobulin and Mitogen-Induced Blastogenesis in Calves^1,2,

Departments of Animal Sciences and Veterinary Clinical Medicine and Surgery, Washington State University, Pullman 99164

ABSTRACT

Fifty-six Holstein calves were used to investigate effects of heat and cold stressors on mitogen-induced blastogenesis of isolated peripheral blood mononuclear cells and immunoglobulins G₁ and M in blood plasma. Calves were exposed to constant hot (35° C), constant cold (—5°C), or thermoneutral (23°C) ambient conditions in environmentally-controlled chambers. Immune responses were measured soon after introduction into environmental chambers (3 days) and after various degrees of adaptation (7 and 14 days). Mortality was greater among heat- and cold-exposed calves than among thermoneutral calves. Neither heat nor cold exposure had a direct effect on blastogenesis of peripheral blood mononuclear cells by phytohemagglutinin or concanavalin A. Plasma from heat and cold-exposed calves then was incorporated into the culture medium at a final concentration of 5% and tested in a mitogenesis assay on peripheral blood mononuclear cells from a single healthy donor. Plasma from heat-exposed calves consistently enhanced tritiated thymidine incorporation into normal peripheral blood mononuclear cells by phytohemagglutinin and concanavalin A as compared to plasma from cold-exposed calves. After heat exposure for 3 to 14 days, immunoglobulin G1 averaged 27% less in heat-exposed calves than in calves that were held at thermoneutrality, but M was unaffected. Cold exposure did not have a consistent effect on G: or M. These data demonstrate that chronic heat and cold stressors affect calves by altering both antibody-and cell-mediated immunity.

¹ Published as Scientific Paper No. 5842. College of Agriculture Research Center, Washington State University, Projects 0344 and 0492.

² Project supported by PL 95-113, USDA, to K. W. Kelley and J. F. Evermann.

³ Department of Animal Sciences.

⁴ Department of Veterinary Clinical Medicine and Surgery.