Effect of fiber source and a yeast culture (Saccharomyces cerevisiae1026) on digestion and the environment in the rumen of cattle

The objective of this study was to determine the effect of fiber source (alfalfa hay, coffee hull, cornstalk) with or without a yeast culture (Saccharomyces cerevisiae1026; YS) on in situ digestion and the environment in the rumen of cattle. Six ruminally cannulated Holstein steers (484 kg BW) were randomly assigned to three diets within a 6 × 6 Latin square: Diet 1 (control): 37% sorghum grain (SG), 14% dried poultry waste, 5% cane molasses and 40% alfalfa hay (AH); Diet 2: coffee hull (CH) replaced 50% of AH; Diet 3: cornstalk (CS) replaced 50% of AH; plus YS (10 or 0 g per head per day). Potentially digestible DM (PDDM), NDF (PDNDF), and CP (PDCP) were measured sampling dacron bags at 0, 3, 6, 12, 24, 48 and 72 h of in situ incubation. Ruminal fluid samples were taken at 0, 3, 6 and 12 h to determine rumen pH (to calculate pH-hours below 6.2), and concentration of VFA and N-NH3. There were no effects (P > 0.05) of YS or fiber source on PDDM, PDNDF, and PDCP degradation rates for AH, SG and CD. Addition of YS to AH increased (P < 0.05) PDNDF (70.2 vs. 56.1%) and PDCP (79.5 vs. 71.4%). For SG the yeast culture increased (P < 0.05) PDDM (94.7 vs. 90.7%), PDNDF (66.4 vs. 50.7%) and PDCP (85.7 vs. 81.2%) when AH was the fiber source. For complete diets with AH as fiber source, the addition of YS increased (P < 0.05) PDNDF (55.0 vs. 46.6%) and PDCP (90.2 vs. 85.7%). Rumen pH was similar but pH-hours below 6.2 were decreased (P < 0.05) by the yeast culture for AH and CS. Addition of YS increased (P < 0.05) N-NH3 ruminal concentration (mg per 100 ml) for AH (36.3 vs. 27.7%), CH (36.4 vs. 26.9%) and CS (36.5 vs. 28.2%); also, YS increased (P < 0.05) VFA concentration for AH (88.2 vs. 74.3 mM) and CH (69.6 vs. 51.7 mM). There were no differences among fiber sources, whereas the yeast culture improved PDDM, PDNDF and PDCP for AH, and also for SG and CD when alfalfa hay was the fiber source.