PSVIII-18 - Nutrient Digestibility of Feedlot Beef Yearling Steers Offered Finishing Diets with Direct Fed Microbial Mixtures

Abstract: The effects of dietary inclusion of live bacteria on feedlot beef cattle apparent total tract nutrient digestibility were evaluated. Crossbred-Angus yearling steers (n = 192; initial BW = 409 kg ± 8 kg) were blocked by body weight (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 containing the following treatments: 1) Control, in which no direct fed microbial (DFM) was offered (lactose as carrier only); 2 and 3) Probiotic mixtures at distinct concentrations [Mixture A and B, at 2g/animal-daily (lactose used as carrier)]. Orts DM were quantified (if any) daily and subtracted from total dietary DM offered to calculate DM intake. Fecal samples were collected twice daily (0700 and 1700 h) for 5 consecutive days (d 68 to 72) from at least 3 steers per pen, while feed samples were collected daily. Samples were composited within period, dehydrated (55°C), and ground (1mm) for further analyses. Total fecal output was estimated with a dietary internal marker (288-h indigestible NDF) and used to calculate nutrient digestibility. Data were analyzed using the GLIMMIX procedure of SAS and pen was considered the experimental unit. Intakes of DM, OM, NDF, and ADF during the digestibility assessment were not affected (P ≥ 0.13) by treatments. Steers offered DFM mixture-A tended to increase digestibility of DM (P = 0.07; 79.3 vs. 77.1%), NDF (P = 0.10; 56.9 vs. 51.6%), and hemicellulose (P = 0.08; 59.4 vs. 53.9%) compared with control, while digestibility of ADF was not affected (P = 0.24) by treatment. The DFM mixture-A seemed to positively affect apparent digestibility of nutrients in steers consuming a steam-flaked corn-based finishing diet, in which improvements in the fiber fraction digestion seemed to be a meaningful contributor.