摘要：Background and Objective: Modifying rumen fermentation using plant secondary metabolites has long been used as a nutritional strategy to improve feed efficiency and it leads to higher livestock productivity. An essential oil (EO) is a plant secondary metabolite with volatile characteristics that has various bioactive compounds and plays an important role in manipulating the fermentation process in the rumen and modifying feed efficiency. The aim of the study was to observe the effect of lemongrass leaves ( Cymbopogon citratus ), which are Indonesian herbs containing an essential oil (EO), as potential agents to manipulate rumen fermentation and to observe their effects on the rumen microbial population and nutrient digestibility in an in vitro system. Methodology: Five inclusion levels of lemongrass leaves (LEM), which were equal to the EO levels of 0, 25, 50, 75 and 100 mg L1 on a DM basis, were added to a diet consisting of king grass and rice bran (40:60). An in vitro rumen fermentation method was used to determine nutrient digestibility and anaerobic inoculations were used to determine the total microbial count. All of the treatments were replicated five times and the collected data included the total rumen microbial population count, total protozoa count, dry matter digestibility (DMD), organic matter digestibility (OMD), crude protein digestibility (CPD) and crude fiber digestibility (CFD). Results: No difference was observed in the total protozoa count; however, an increase in EO supplemented with LEM decreased the total ruminal microorganism count (p<0.001). Furthermore, the inclusion of LEM in the diet affected DMD, OMD and CPD. The inclusion of LEM at 50, 75 and 100 mg L1 decreased (p<0.01) OMD by 5.54, 5.24 and 6.17% and reduced DMD (p<0.01) by 10.02, 9.26 and 11.38%, respectively. Furthermore, there was considerable evidence that supplementation with LEM inhibited deamination, which resulted in low CPD. Interestingly, CFD was not affected by the addition of LEM. Conclusion: The study suggested that LEM caused a reduction in the total number of rumen microbes and that it potentially decreased ruminal digestibility; thus, EO supplemented with LEM should be limited to 25 mg L1.
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