PS8-18. Influence of Bacillus-dfm and Sulfate Trace Minerals on in vitro Digestibility Parameters of Standard Diet for Dairy.

Abstract An in vitro study was conducted to evaluate the effects of a Bacillus-based probiotic and Cu, Mn, and Zn in the form of sulfate (SULF) 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) sulfate (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 SULF); 2) SULF (10, 20, and 30 mg/kg DM of Cu, Mn, and Zn, respectively); 3) BVAC; and 4) BVAC + SULF. 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 was 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. In vitro DMD was affected by treatment (P < 0.0001) and incubation time (P < 0.0001), with no treatment × time interaction (P = 0.08). BVAC increased DMD compared to other treatments. Dry matter digestibility increased over time, with greater values at 24 and 48 h. In vitro pH was not influenced by treatment (P = 0.97) but declined with incubation time (P < 0.0001), reflecting normal fermentation. There was a treatment × time interaction (P = 0.02) for gas pressure. At 6 h, SULF had greater (P < 0.05) gas pressure than other treatments, whereas at 48 h BVAC showed greater (P < 0.05) gas pressure. BVAC improved in vitro DMD without altering pH, while fermentation increased over time with treatment-dependent gas production. For image description, please refer to the figure legend and surrounding text.