Effects of dietary microbial inoculants on beef cattle feedlot growth performance and carcass traits, apparent nutrient digestibility and ruminal characteristics

The effects of the dietary inclusion of a mixture of bacterial direct fed microbials (DFM) on feedlot beef cattle growth performance, carcass characteristics, nutrient digestibility, feeding behavior, and ruminal papillae morphology were evaluated. Crossbred-Angus steers (n = 192; initial BW = 409 kg ± 8 kg) were blocked by BW and randomly assigned into 48 pens (4 steers/pen; 16 pens/treatment) following a randomized complete block design. A steam-flaked corn-based fishing diet was offered ad libitum once daily for 153 d containing the following treatments: 1) Control, in which no DFM was offered (lactose as carrier only, 2 g/animal-daily); 2) Treat-A ( L. animalis DSM33570, P. freudenreichii DSM34127; B. subtilis DSM32324; and B. licheniformis DSM17236, at 1.3; 1.3; 1. 3, and 3.9 × 109 CFU/animal-daily, respectively); and 3) Treat-B, consisting of the same microbial combination, but with doses as follows: 1.3; 1.3; 3.9; and 1.3 × 109 CFU/animal-daily. Data were analyzed using the GLIMMIX procedure of SAS, in which pen was considered the experimental unit with the fixed effect of treatment and the random effect of BW-block, while pre-planned contrasts comparing Control × treat-A or treat-B were performed. Steers offered treat-A increased carcass adjusted ADG (P = 0.03) by 6.7%, gain efficiency (P < 0.01) by 6%, tended (P = 0.07) to increase carcass-adjusted final BW by 15 kg, and hot carcass weight (P = 0.07) by 10 kg, while treat-B did not differ (P ≥ 0.17) from control. Overall DM intake (P = 0.36) and other carcass traits (P ≥ 0.13) were not affected by treatments. Steers offered treat-A tended to increase digestibility of DM (P = 0.07) by 3%, NDF (P = 0.10) and hemicellulose (P = 0.08) by 9% compared to control, while treat-B did not differ (P ≥ 0.10) from control. No treatment × period interactions (P ≥ 0.21) or main effects of treatment (P ≥ 0.12) were observed for feeding behavior. However main effects of phase showed steers ruminated, ate, chewed, and were more active (P ≤ 0.01) during the second behavioral assessment, while more (P < 0.01) time spent ruminating, eating and chewing in minutes per/kg were observed on d 113 vs. 106. Ruminal morphology (P ≥ 0.39) and ruminal ammonia concentration (P = 0.44) were not affected by treatments. Steers offered the DFM treat-A had improved growth performance and it seemed to positively affect carcass quantity, while treat-B did not show similar potential. The DFM combinations did not seem to affect feeding behavior neither ruminal papillae morphology.