Effect and of breed (Angus vs Simmental) on immune function and response to a disease challenge in stressed steers and preweaned calves

Two experiments were conducted with feeder steer calves and preweaned calve s to determine the effects of breed on immune response. In Exp. 1, newly we aned Angus (n = 24) and Simmental (n = 24) steer calves were blocked by wei ght within breed and randomly assigned to 12 pens with four calves per pen. The basal diet consisted of 87% corn silage (DM basis) and 13% of a soybea n meal-mineral-vitamin supplement. Steers were allowed ad libitum access to feed throughout the study. On d 2 following weaning, calves received an in tranasal inoculation of infectious bovine rhinotraecheitis virus (IBRV; 2.7 x 10(8) CCID50). Rectal temperatures in response to the IBRV were higher ( P < .05) in Angus calves. On d 9, calves were injected i.m. with 10 mt of a 25% pig red blood cell (PRBC) suspension. Total immunoglobulin (Ig) and Ig M titers against PRBC were higher (P < .05) for the Angus calves. Breed did affect cell-mediated immune response to phytohemagglutinin (PHA). In Exp. 2, preweaned (16 Angus and 16 Simmental) calves were selected based on bree d, body weight, and sex. On 0 d, all selected calves were injected i.m. wit h 10 mt of a 25% PRBC suspension. Total Ig and IgG titers against PRBC were higher(P < .05) for Angus calves. On d 28, lymphocytes were isolated from peripheral blood obtained from eight calves per breed. Peripheral lymphocyt es from:the Angus calves had a greater (P < .07) blastogenic response to 6. 25 mu g/mL of PHA than lymphocytes from Simmental calves. Results indicate that the immune response of Angus and Simmental calves may differ.