Evaluation of NutraGen®, an immunomodulatory feed additive, in calves subjected to a combination viral and bacterial bovine respiratory disease challenge

Two 89-d experiments evaluated the effects of an immunomodulatory feed additive (NutraGen®; NG) on calf health parameters following a bovine respiratory disease (BRD) challenge as well as the efficacy of a bronchoalveolar lavage (BAL) procedure as a means of confirming and quantifying an experimental Mannheimia haemolytica (MH) challenge in calves. Steers [Experiment 1 (n = 16, initial BW = 271 ± 33.0 kg)] and [Experiment 2 (n = 16, initial BW = 232 ± 33.2 kg)] were blocked by genetic background and randomly allocated to 1 of 3 experimental treatments. Treatments included a placebo (CON; n = 5), NG fed from d -18 to d 28 (PREC; n = 6), and a placebo fed from d -18 to d -3 followed by NG fed from d -3 to d 28 (CHLG; n = 5). Data were analyzed using the GLIMMIX procedure of SAS Version 9.4 (SAS Institute, Cary, N.C.). The feeding of NG impacted respiration rate (RR; P ≤ 0.05), increased serum glucose (GLU) and lactate (L) production (P < 0.01), increased leukocyte (LEU) concentrations (P < 0.0001), decreased neutrophil (NEU) and increased lymphocyte (LYM) concentrations (P ≤ 0.05), altered serum MH antibody production (P = 0.06), and altered serum IL-10 concentrations (P ≤ 0.07). No active pre-challenge MH growth was observed in any of the enrolled animals. The analysis of post-challenge BAL fluid sample sets on d 6 of each experiment confirmed a minimum active MH growth of 1.67E+01 cfu/mL in 37% of inoculated steers. No statistical difference was observed between steers that did or did not have detectable MH growth post-MH challenge or rectal temperature, clinical score, or serum MH antibody titers. Overall, these experiments suggest that NG has the potential to alter certain clinical and cellular responses in calves exposed to a BRD pathogen challenge. While the collection of BAL samples may hold value as a clinical diagnostic tool, it is not recommended that BAL procedures be used to quantify bacterial overgrowth or infection in the lung of steers exposed to pathogens of the BRD complex in a research or experimental setting.