Rambutan fruit peel powder and dietary protein level influencing on fermentation characteristics, nutrient digestibility, ruminal microorganisms and gas production using in vitro fermentation techniques.

The objective of this study was to evaluate the effect of rambutan (Nephelium lappaceum) fruit peel powder (RP) on fermentation characteristics, rumen microorganisms, and in vitro gas production. Three levels of crude protein (CP) in the concentrate (14%, 16%, and 18% CP) and supplementation of rambutan peel powder (0, 2, 4, and 6% of the total dietary substrate) were designed for treatments according to 3 × 4 factorial arrangement in a completely randomized design (CRD). The rumen fluid samples were collected from two-fistulated dairy bulls which had been fed on rice straw with concentrate to adjust the rumen environment. The ratio of roughage (R) and concentrate (C) at 60:40 was used, and all ingredients were added according to the mentioned ratio, respectively. Under this study, supplementation of CP at different levels in the concentrate diet significantly altered (P < 0.05) rumen NH3 -N at 6 and after 12 h of incubation, whereas the rumen pH was not significantly changed with CP and RP supplementation levels at any times of incubation. The rumen pH was declined at 18% CP at 6 h of incubation time, as compared to 14 and 16% CP with 0% RP supplementation. The CP and RP supplementation could enhance and maintain the rumen pH during incubation to the optimum condition. The RP supplementation significantly doubled bacterial population while reduced protozoal population; however, fungal zoospores were not altered with CP and RP supplementation. The ruminal propionate (C3 ) production was remarkably higher (P < 0.05) by the RP and CP supplementation. The ratio of acetate to propionate (C2 :C3 ) was decreased (P < 0.05) with RP supplementation. Meanwhile, rumen methane (CH4 ) production was significantly reduced by the RP supplementation. In addition, high level of RP supplementation (6% of total substrate) also significantly decreased the cumulative gas production and the in vitro true digestibility (%IVTDMD). Level of CP had no effect on rumen fermentation while interactive effects of CP level and RP supplementation were not found. This current study indicated that RP supplementation could suppress protozoal population, mitigate methane production, and improve rumen fermentation.