Effects of four ruminant feed additives on in vitro ruminal fermentation kinetic gas production and degradability

Abstract Text: This experiment was designed to investigate the effects of four ruminant feed additives, Bacillus subtilis, procreatin (major ingredient was high-enriched live yeast), Aspergillus oryzae culture and fibrase (major ingredient was Aspergillus oryzae, Aspergillus niger and lactic acid yeast) on gas production (GP) kinetics of different doses of 0(control), 1.0, 2.0, 4.0mg/kg diet (DM), respectively. Ruminal fluid was collected approximately 2 h before feeding from three lactating Holstein dairy cows (BW= 558±10 kg, DIM = 153 ±16d ) fed total mixed ration (C:F = 40:60) and mixed with McDougall’s phosphate buffer (v/v=1:2). 500mg diet substrates, which were consistent with the donor cows, were incubated with diluted buffered rumen fluids (75ml) for 72 h at 39°C. The batch completed in 2 experimental runs, and 4 fermentations per treatment were arranged in each run. All bottles were connected to gas channel inlets of Automated Trace Gas Recording System for Microbial Fermentation (AGRS, Beijing, China). Data on the cumulative gas production were fitted to a model: GP_t (ml/g DM)=A/(1+(C/t)^B). Where GP_t was the cumulative gas production (ml/g DM) at t incubation time (h), A was the asymptotic gas production (ml/g DM), B was a sharpness parameter determining the shape of the curve and C was the time (h) at which half of A is reached. A, B and C were calculated by the nonlinear procedure of SAS. There was no difference of C in all treatments (P > 0.05). Regarding to Bacillus subtilis, the GP₇₂ (P = 0.08), A (P = 0.09) tended to linearly decrease with increase of adding levels, while B tended to increase (P = 0.06). For procreatin, the GP₇₂ (P = 0.06) tended to quadratically increase and A quadratically increased (P < 0.05), however, the doses did not affect B (P > 0.05). The addition of Aspergillus oryzae linearly increased the GP₇₂ (P < 0.01) and A (P < 0.01) and had a tendency for B (P = 0.09). The GP₇₂ (P < 0.05) and A (P < 0.05) linearly increased with the rise of fibrase addition levels and no difference in B. In vivo digestibility of animal feeds was estimated by measuring in vitro GP of feed samples incubated in ruminal fluid buffered. The results suggested that Aspergillus oryzae and fibrase addition could increase the extent and rate of feed degradation while Bacillus subtilis and procreatin addition had slightly effects.

Keywords: feed additives, gas production, in vitro