ABSTR•Cr.-We investigated the effects of dietary protein quality on the development and functioning of the immune system in four-week-old Northern Bobwhite (Colinus virginianus) chicks. Chicks were fed isocaloric diets containing 8, 15, or 33% protein over a three-week period. Significant reductions in the rate of body growth were evident in chicks receiving 8 and 15% protein. Development of the bursa of Fabricius and spleen was significantly depressed in the 8% protein group compared to the other two treatments. Lymphocyte yields from dissociated lymphold organs of chicks fed 8% protein were substantially reduced compared to birds fed higher levels of protein. In vitro lymphoproliferative responses of cultured splenocytes to mitogenic stimulation (concanavalin A, pokeweed mitogen, and Salmonella typhimurium), white-blood-cell counts, and in viva measures of humoral immunity did not differ among dietary treatments. Cell-mediated immune function, as measured by an in viva hypersensitivity response to an intradermal injection of a T lymphocyte-dependent mitogen (phytohemagglutinin), was significantly suppressed in the 8% protein group compared to the other two treatments. Several measures of immune-system development and function were significantly correlated with body mass change during the trial. Results indicated that four-week-old Northern Bobwhite chicks fed an 8% protein diet for three weeks may have difficulty expressing a competent immune response to pathogenic challenge in the wild.

We examined the hypothesis that environmentally induced alteration of immunocompetence is a primary physiological mechanism by which population survival is regulated. The involvement of disease and immunocompetence in the regulation of small mammal populations is not well understood but a strong relationship between physiological stress and immunity has been demonstrated. Its involvement is further supported by several studies, which have provided evidence that survival, incidence of disease, and selected gross measures of immunity change temporally with density and season. We examined this hypothesis by documenting the existence of temporal alterations in selected measures of both humoral and cell—mediated immune function in a population of cotton rats (Sigmodon hispidus), a species known to fluctuate widely in density, inhabiting a tallgrass prairie in central Oklahoma. A total of 310 cotton rats was collected from August 1989 to May 1991 (10 collections) using conventional live—trap methods. In addition to morphological characteristics of primary and secondary lymphoid organs, the ability of splenocytes to produce specific antibody in response to a single injection of sheep erythrocytes and to proliferate in response to in vitro exposure to mitogens was measured to assess immunocompetence. Whole blood was collected for the determination of total peripheral blood leukocyte counts, packed cell volume, and total serum proteins. Statistically significant differences in all variable except total serum protein existed among the 10 collections and most of this variability was independent of specific seasonal time periods. Bimodal thythmicity was characteristic of temporal changes for several measures of immunocompetence. Changes over time in the average immunocompetence of this population could have reflected a shift in genotypic polymorphism; several other plausible explanations are offered to explain the observed temporal patterns.

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