PS8-17. Influence of Bacillus-dfm and Hydroxy Trace Minerals on In Vitro Digestibility Parameters Using a Dairy Diet as Substrate.

An in vitro study was conducted to evaluate the effects of a Bacillus-based probiotic (BVAC) and Cu, Mn, and Zn in the form of hydroxy trace minerals (HTM) on digestibility parameters of a dairy diet formulated for a high producing dairy cow as substrate. A completely randomized design with a 2 x 2 factorial arrangement of treatments was used. Factors included: 1) BVAC (0.0 or 3 g of B. licheniformis and B. subtilis per 70 L of ruminal fluid) and 2) HTM (no supplemental Cu, Mn, or Zn or 10, 20, and 30 mg/kg DM of Cu, Mn, and Zn, respectively). Treatments consisted of: 1) Control (CTRL; no supplemental BVAC or HTM); 2) HTM (10, 20, and 30 mg/kg DM of Cu, Mn, and Zn, respectively); 3) BVAC; and 4) BCVA + HTM. Two hours post feeding, ruminal fluid was obtained from three steers fitted with ruminal cannula. Steers were fed the dairy 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. Dry matter digestibility was greater (P < 0.0001) for HTM, BVAC, and BVAC + HTM than CTRL, suggesting improved ruminal DMD when BVAC and HTM were included. In vitro pH was not affected by treatment (P = 0.4665) but declined over time (P < 0.0001), reflecting normal in vitro fermentation dynamics. There was a treatment x time interaction (P = 0.04) for gas pressure. At 12 h post incubation gas pressure was lower in BVAC compared to all other treatment. However, at 24 h post incubation, HTM, BVAC and HTM + BVAC had greater gas pressure than CTRL. Overall, BVAC and HTM improved in vitro DMD. For image description, please refer to the figure legend and surrounding text.