Objectives were to evaluate how dietary energy intake and source affect immune competence and response to an infectious bovine rhinotracheitis virus (IBRV) challenge in cattle. Forty-eight crossbred beef steers were stratified by body weight within two periods and randomized to 1 of 3 dietary treatments (8 steers/treatment within period). Treatments were: a 70% concentrate diet fed ad libitum (70. AD); a 30% concentrate diet fed ad libitum (30. AD); and 70% concentrate diet restricted to the net energy for gain intake of 30AL (70RES). Ex vivo immune responses were evaluated after treatments were applied for 28 d, after which cattle were moved into individual pens (d 28 to 40) and intranasally challenged with IBRV on d 30. On d 34, all cattle were offered a 50% concentrate diet ad libitum until d 50. Both energy source (P<0.02) and intake level(P<0.04) affected peripheral blood mononuclear cell synthesis of tumor necrosis factor-α, with cell culture supernatant concentrations averaging 2264, 1887, and 1241 pg/mL for 70. AD, 70RES, and 30. AD, respectively. Neither whole blood killing of Mannheimia haemolytica nor neutrophil oxidative burst in response to M. haemolytica was affected by treatments. Serum neutralizing IBRV antibody titers were not different among treatments either before or after the IBRV challenge. Rectal temperature following IBRV peaked 3 d after the IBRV challenge and returned to baseline by d 6, but it was not affected by treatment. No differences were observed in dry matter intake among treatments while the cattle were individually penned and fed a 50% concentrate diet from d 34 to 40. When cattle were group-penned from d 40 to 50 of the study (d 10 to 20 after the IBRV challenge), the 70RES cattle had greater DMI (P<0.04) than cattle in the other two groups. Following the IBRV challenge, serum glucose concentrations did not differ among treatments; however, the 70. AD cattle had greater blood urea N concentrations (P<. 0.01). There was a treatment × time interaction (P<. 0.01) for non-esterified fatty acids, such that cattle fed the 70. AD had increased non-esterified fatty acids on d 3 and 5 after the IBRV challenge. Results indicate that cattle fed diets with a greater energy concentration and to an extent a greater percentage of concentrates had a more pronounced pro-inflammatory response, but other aspects of innate immune responses were not influenced by intake or source of energy.
- Receiving cattle