Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2008
Publication Date: 7/31/2008
Citation: Reuter, R., Carroll, J.A., Dailey, J.W., Cook, B., Galyean, M. 2008. Effects of dietary energy source and level and injection of tilmicosin phosphate on immune function in lipopolysaccharide-challenged beef steers. Journal of Animal Science. 86:1963-1976. Interpretive Summary: A collaborative study was conducted involving scientists from the Livestock Issues Research Unit, Texas Tech University, and The Noble Foundation to evaluate the potential interactions of dietary energy concentration and/or intake and metaphylactic antibiotic treatment on the immune response of beef calves. Specifically, the objective was to determine the separate effects of dietary energy source and energy concentration, with or without administration of an antibiotic, on the acute-phase response to an E. coli lipopolysaccharide (LPS) challenge in beef steers. Results of this experiment indicate that decreasing the diet concentrate:roughage ratio increased production of pro-inflammatory cytokines in response to the LPS challenge in beef steers. A portion of this response seemed to be caused by decreased energy intake, whereas the remainder seemed to be a direct effect of the ingredients themselves (e.g., grain vs. roughage). In addition, administration of antibiotics accelerated the fever response to the LPS challenge. Antibiotic administration elevated pre-challenge concentration of pro-inflammatory cytokines, and decreased serum amyloid-A profiles following the challenge in cattle on a lower energetic plane of nutrition, but not in cattle on a higher plane. Consideration of potential immunomodulating effects of diets and how those effects might interact with cattle that have already been treated for disease may be warranted in future studies. Additional research is needed to confirm our results and to determine the effects of the intensity of pro-inflammatory response on cattle health in a commercial environment. The results of this research will be of particular interest to beef cattle feedlot managers, veterinarians managing the health of feedlot cattle, and scientists, whether from industry, academia, or industry working in the area of beef cattle production, health, well-being, and alternative management practices.
Technical Abstract: Twenty-four Angus x Hereford crossbred steers (247 ± 2.4 kg BW) were used in a completely random design to evaluate the effect of energy source and level with or without antibiotic administration on measures of immune function. Steers were offered 1 of 3 dietary treatments: a 70% concentrate diet ad libitum (70AL); a 30% concentrate diet ad libitum (30AL); and a 70% concentrate diet offered in an amount calculated to provide NEg intake equal to the 30AL treatment (70RES). Half the steers in each dietary treatment received either a s.c. injection of tilmicosin phosphate (ANTI; 1 ml/30 kg of BW) or an equal volume of saline s.c. (SAL). Steers were offered their respective treatment diets for 28 d and administered the ANTI or SAL injections 2 d before an indwelling catheter was placed in the jugular vein, and 2.0 ug/kg of BW of E. coli lipopolysaccharide (LPS) was administered i.v. Blood serum was collected at 30-min intervals from -2 h to 6 h, and at 8, 12, 24, 48, and 72 h relative to the LPS challenge. Increased energy intake (70AL) increased (P less than or equal to 0.04) DMI, ADG, and rectal temperature (RT) following the challenge compared with the 70RES treatment. The 30AL treatment increased the maximum concentrations and area under the response curve of the proinflammatory cytokines (PIC) interferon gamma (INFgamma), tumor necrosis factor-alpha (TNFalpha), and IL-6 (P less than or equal to 0.05) compared with the average of the 70AL and 70RES treatments. Decreasing energy intake (70RES vs. 70AL) increased IL-6 (P less than or equal to 0.003) and numerically increased INF gamma and TNF alpha (P less than or equal to 0.34 and 0.14, respectively) following LPS administration. Tilmicosin decreased the time to attain maximum RT (P = 0.01) by 1 h without altering the peak RT (P = 0.85), and tilmicosin interacted with energy intake to increase pre-challenge PIC in 70RES vs. 70AL (P less than or equal to 0.05). Results suggest that increased PIC response, presumably resulting from a combination of decreased energy intake and from direct effects of roughage, may be a mode of action for the slight decrease in morbidity that often occurs when newly received, stressed calves are fed receiving diets high in roughage. Antibiotics may have immunomodulatory capacity beyond their direct effects on pathogenic bacteria, and these effects could interact with dietary energy intake.