Effects of bacterial direct-fed microbial combinations on beef cattle growth performance, feeding behavior, nutrient digestibility, ruminal morphology, and carcass characteristics

The effects of the dietary inclusion of a mixture of bacterial direct-fed microbial (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 body weight (BW) = 409 kg +/- 8 kg) were blocked by BW and randomly assigned into 48 pens (4 steers/pen and 16 pens/treatment) following a randomized complete block design. A steam-flaked corn-based fishing diet was offered to ad libitum intake once daily for 153 d containing the following treatments: (1) Control (no DFM, lactose carrier only); (2) treat-A (Lactobacillus animalis, Propionibacterium freudenreichii, Bacillus subtilis, and Bacillus licheniformis), at 1:1:1:3 ratio, respectively; totaling 6 x 10(9) CFU (50 mg)/animal-daily minimum; and (3) treat-B, the same DFM combination, but with doses at 1:1:3:1 ratio. Bacterial counts were similar to 30% greater than the minimum expected. Data were analyzed using the GLIMMIX procedure of SAS, with pen as the experimental unit, the fixed effect of treatment, and the random effect of BW-block, while preplanned contrasts comparing Control x treat-A or treat-B were used. Steers offered treat-A had increased carcass-adjusted average daily gain (P = 0.03) by 6.7%, gain efficiency (P < 0.01) by 6%, tended (P = 0.07) to have increased 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 dry matter (DM) intake (P = 0.36) and other carcass traits (P >= 0.13) were not affected by treatments. Steers offered treat-A tended to have increased digestibility of DM (P = 0.07) by 3%, neutral detergent fiber (P = 0.10), and hemicellulose (P = 0.08) by 9% compared with control, while treat-B did not differ (P >= 0.10) from control. No treatment x period interactions (P >= 0.21) or main effects of treatment (P >= 0.12) were observed during 24-h feeding behavior. Steers ruminated, ate, chewed, and were more active (P <= 0.01) during the second behavioral assessment (day 113), while drinking behavior was not affected (P >= 0.88). Ruminal papillae morphology and ruminal ammonia concentration (ruminal fluid collected at slaughter facility) were not affected by treatment (P >= 0.39). Steers offered the DFM treat-A had improved growth performance and it positively affected carcass weight and nutrient digestion. The DFM combinations did not seem to affect feedlot cattle feeding behavior or ruminal papillae morphology. Lay Summary Direct-fed microbials (DFM) are naturally occurring microorganisms that alter cattle ruminal fermentation and intestinal function and have been shown to improve growth performance and nutrient digestibility of cattle. The use of DFM in animal feed has continuously increased in feedlots as an alternative to traditional antibiotic additives, which have gained negative public perception and additional regulatory scrutiny. High-energy diets can induce physiological challenges to cattle, especially when based on high starch availability ingredients, which may negatively affect animal growth performance. Such physiological digestive challenges may be overcome by a target combination of DFM bacterial strains (Lactobacillus animalis, Propionibacterium freudenreichii, Bacillus subtilis, and Bacillus licheniformis). These microorganisms individually have shown to have positive effects on finishing cattle offered high-energy diets, which highlights the need for research to optimize DFM types and doses to enhance the use of bacterial strains that can positively affect cattle growth performance, carcass traits, nutrient digestibility, and other variables relevant to the physiology of digestion. In the current experiment, feedlot steers offered a specific bacterial DFM combination/dose had improved average daily gain and feed efficiency, which were reflected as a positive influence on hot carcass weight and digestibility of nutrients, while not effectcting feeding behavior and ruminal morphology.