175. Influence of Bacillus-DFM and Trace Minerals Sources on In Vitro Digestibility Parameters of a Feedlot Diet.

Abstract Influence of Bacillus-DFM and trace minerals sources on in vitro digestibility parameters of a feedlot diet. An in vitro study was conducted to evaluate the effects of a Bacillus-based probiotic and trace minerals source on in vitro fermentation characteristics using a standard high concentrate feedlot diet as substrate. A completely randomized design was used. Treatments included: 1) Control - no Bacillus (BVAC) and no Trace Minerals (TM); 2) BVAC; 3) Hydroxy Trace Minerals (HTM); BVAC + HTM; 5) Sulfate (SULF) and 6) BVAC + SULF (TM, HTM or SULF: Cu, Mn, or Zn with 10, 20, and 30 mg/kg DM respectively and BVAC: 3 g of B. licheniformis and B. subtilis per 70 L of ruminal fluid). Two hours post feeding, ruminal fluid was obtained from three steers fitted with ruminal cannula. Steers were fed the dairy the diet for 21 d prior to rumen fluid collection. The basal diet was ground to fit through a 2 mm screen and used as the substrate for in vitro incubations. Substrate (0.5 g) was incubated in 70 mL of a 1:1 mixture of ruminal fluid and McDougall’s buffer, at 39°C in a circulating water bath, in vaccine bottles. Vaccine bottles were purged with CO2, capped and sealed immediately after the McDougall’s buffer/rumen fluid mixture was added. Vaccine bottles remained sealed to maintain anaerobic conditions and were incubated for 6, 12, 24, and 48 h in triplicate for each treatment at each timepoint. To simulate rumen motility, vaccine bottles were gently swirled every 4 h. At the appropriate timepoints, vaccine bottles were removed from the water bath, gas pressure was recorded, pH determined, and then centrifuged at 28,000 x g. Following centrifugation, the supernatant decanted and the remaining digesta was dried at 100°C for 72 h and weighed to calculate DM disappearance (DMD). Data were analyzed as a completely randomized design using the GLM procedures in SAS. There were no treatment x time interactions (P > 0.05) for any of the response variables measured. Treatment and time affected (P < 0.05) DMD, pH, and gas pressure. Dry matter digestibility was greater (P < 0.05) in BVAC + HTM compared to all other treatments. In vitro pH was impacted by treatment. In vitro pH was greater (P < 0.05) in SULF compared to BVAC. Overall, BVAC combined with HTM improved in vitro DMD. For image description, please refer to the figure legend and surrounding text.