332 Selection for moderate and high growth and dam age differentially affect immune and stress responses of beef calves at weaning

Pressure for intense genetic selection of important economic traits has impacted several robustness traits in cattle including immune function, which can impact animal health and well-being. Furthermore, maternal traits like age and health status can influence passive immunity and, therefore, progeny immune status. This study aimed to determine the effect of genetic selection for moderate or high growth and dam age on immune phenotype and stress response of beef calves at weaning and 14 d post-weaning. Fall-born calves selected and sired by bulls of either moderate (MG, n = 23) or high (HG, n = 23) growth were used. Body weights and blood samples were taken at weaning (6 to 7 mo of age) and 14 d post-wean (14DPW). Samples were processed and analyzed for cortisol, immunoglobulins (Ig), lymphocyte proliferation, complete blood counts, and cytokines. Dam age was categorized into one of four age classifications: Heifer (2 yr, n = 8), Young (3-4 yr, n = 17), Mid (5-6 yr, n = 11), and Old (7+ yr, n = 12). Data were analyzed using PROC GLM (SAS 9.4). A dam age × growth trait interaction occurred for several measures, including neutrophils (P < 0.01), lymphocytes (P < 0.01), neutrophil-to-lymphocyte ratio (P < 0.001) and several cytokines (P < 0.05). The HG-sired calves from Heifer dams had greater numbers and percentages of neutrophils, less percentage of lymphocytes, and a greater neutrophil-to-lymphocyte ratio than calves from Young and Mid Dams and their MG counterparts. Conversely, pro-inflammatory cytokine concentrations, including IL-6 and IL-17A, were greater in MG-sired calves from heifer dams than those from the other dam ages. Main effects of growth or age on immune measures and body weight were also found. Serum IgG1 (P = 0.0003), IgG2 (P = 0.0031), and total IgG (P = 0.001) concentrations and Concanavalin A-induced lymphocyte proliferative response (P < 0.05) were greater among MG-sired calves than HG ones. At 14DPW, neutrophil-to-lymphocyte ratio was greater (P < 0.01) in HG-sired calves than MG ones, and HG calves were also heavier at weaning and 14DPW (P = 0.0020). Calves born to Old dams were heaviest than calves in all other dam age groups (P = 0.0039). These data infer that not only does genetic selection for high or moderate growth impact calf immune function, but maternal influence of age also differentially affects the immune phenotype.