Conditions stimulating neutral detergent fiber degradation by dosing branched-chain volatile fatty acids. II: Relation with solid passage rate and pH on neutral detergent fiber degradation and microbial function in continuous culture

To support improving genetic potential for increased milk production, intake of digestible carbohydrate must also increase to provide energy and microbial protein synthesis. We hypothesized that the provision exogenous branched-chain volatile fatty acids (BCVFA) would improve both neutral detergent fiber (NDF) degradability efficiency However, BCVFA should be more beneficial with increasing bacterial synthesis associated passage rate (kp). decreasing pH need isobutyrate over 2-methylbutyrate. study these effects independent from other sources variation in vivo, we evaluated continuous cultures without (control) versus (0 vs. 2 mmol/d each isobutyrate, isovalerate, 2-methylbutyrate), low high kp particulate phase (2.5 5.0%/h), (ranging 6.3 6.8 diurnally 5.7 6.2) a × factorial arrangement treatments. Diets were 50% forage pellets grain administered twice daily. Without an interaction, NDF tended 29.7 35.0% main control compared Provision methanogenesis, presumably resulting improved degradability. Decreasing decreased methane production. Total acid (VFA) acetate production kp, even though true organic matter nitrogen flow not affected by but propionate valerate probably shift taxa VFA stoichiometry. isovalerate while 2-methylbutyrate on net basis (subtracting doses). Supplementing moderate (15.4%) crude diets (excluding urea buffer) major interactions culture kp.