Immune responsiveness and lymphoreticular morphology in cattle fed hypo- and hyperalimentative diets.

Immune responses and lymphoreticular morphology were studied in 3 groups of yearling Hereford steers fed hypoalimentative, maintenance and hyperalimentative diets for 142 days. Significant decreases in plasma protein levels and circulating lymphocyte levels occurred in low energy intake steers. Percent circulating lymphocytes bearing surface immunoglobulins and serum levels of IgG and IgM did not vary significantly within or between groups. Antibody responses to Brucella abortus bacterin inoculated on day 63 were similar in all 3 groups. Antibody responses to chicken erythrocytes inoculated on day 88 were significantly lower in hypoalimentated steers. Differences between groups in lymphocyte blastogenic responses to phytohemagglutinin (PHA), concanavalin A (Con A) and pokeweed mitogen (PWM) were not significant. Hyperalimentated steers had significantly depressed PWM responses compared to a baseline value established for that group. In addition, hypoalimentated steers tended to have elevated responses to PHA, although differences were not significant. There were no significant differences between groups in dermal hypersensitivity responses to tuberculin following sensitization with viable Bacillus Calmette-Guerin (BCG). The thymuses of hypoalimentated steers were markedly atrophied but lymph nodes and splenic white pulp were normal. Thymus, lymph nodes and spleen were normal in hyperalimentated steers.