Response of rumen fermentation to urease inhibitor using dual-flow rumen simulation system
The objective of this study was to investigate urea degradation using a novel dual-flow rumen simulation system. Eight fermentation vessels (1 L) were allotted to a 2 × 2 factorial arrangement of treatments with urea supplemented at 0 or 0.5% dry matter intake (DMI), and urease inhibitor equivalent to 0 or 450 mg/kg DMI. A total of 40 g of DM with urea were fed in two equal portions daily, while the urease inhibitor, contained approximately 98% (w/w) acetohydroxamic acid (AHA), was added in the artificial saliva infused into the vessels twice daily. The experimental period consisted of 6 days for adaptation and 3 days for sampling. On each sampling day 15 mL fermentation fluids were obtained from each fermentation vessel by syringes at 0, 2, 4, 6, 8, and 10 h, respectively. Temperature (39℃), liquid, and solid dilution rates (8%/h and 200 mL/d, respectively) were maintained through the whole process. Both protozoa numbers and dry matter disappearance (DMD) (P = 0.62 for urea; P = 0.47 for AHA) from each fermentation vessel were not affected by urea or AHA supplementation. Urea supplementation significantly (P < 0.01) increased pH and ammonia-nitrogen (NH3-N) concentration, and AHA addition increased (P = 0.03) urea-N concentration. There was no interaction between urea and AHA. The pH reached the peak value at 2 h with urea supplementation only, and the pH began to reduce at 4 h with both urea and AHA addition. NH3-N concentration arrived at maximum at 2 h with urea and/or AHA supplementations, but it sharply (P< 0.05) decreased at 4 h with urea supplementation and at 6 h with both urea and AHA addition. Urea-N concentration of treatment with urea and AHA supplementation was sustainably higher than other treatments until 6 h. It was concluded that AHA inhibited urea degradation but had no effect on ammonia formation.
Keywords: dual-flow rumen simulation system, fermentation, urease inhibitor