Immune responsiveness, lymphoreticular morphology, and infectious bovine rhinotracheitis susceptibility in cattle fed low and high energy rations

Abstract

Clinical responses, general immune responsiveness, and lymphoreticular morphology were studied in 3 groups of yearling Hereford steers fed at low energy levels, maintenance energy levels, and high energy levels for 141-144 days. Clinical and immunologic responses to virulent infectious bovine rhinotracheitis virus administered on day 117 were also studied. Average daily weight loss in low energy intake steers was 0.52 kg. Average daily weight gain in maintenance energy intake steers was 0.18 kg and in high energy intake steers, 1.07 kg. Significant decreases in rectal temperatures, plasma protein levels, packed cell volumes, and circulating leukocyte, lymphocyte, and neutrophil levels occurred in low energy intake steers. Percent circulating lymphocytes bearing surface immunoglobulins did not vary significantly within or between groups. There were no significant differences in serum IgG and IgM levels within or between groups. Antibody responses to Pasteurella hemolytica bacterin inoculated on days 3, 60, and 133 and to Brucella abortus bacterin inoculated on day 63 were similar in all 3 groups. Antibody responses to chicken erythrocytes injected on day 88 were significantly lower in low energy intake steers. Differences between groups in in vitro lymphocyte blastogenic responses to phytohemagglutinin, concanavalin A, and pokeweed mitogen were rarely and inconsistently significant. In addition, group lymphocyte blastogenic responses rarely differed significantly from previously established baseline values. An exception was the consistently and significantly depressed pokeweed mitogen responsiveness which occurred in high energy intake steers. Antigen specific in vitro lymphoproliteration was not detected following inoculation with keyhole limpet hemocyanin and with viable Bacillus Calmette-Guerin but in vivo delayed hypersensitivity skin responses to these antigens were elicited in all steers. Skin responses to intradermal injection of phytohemagglutinin, concanavalin A, and pokeweed mitogen on day 104 were detected in all steers by microscopic examination of testsite biopsies and were suggestive of delayed hypersensitivity. There were no significant differences between groups in neutrophil phagocytic capabilities...