عنوان مقاله [English]
نویسنده [English]چکیده [English]
Introduction: Nowadays, using antibiotics in ruminant feeding as growth promoters has been restricted due to the appearance of multi-drug resistant bacteria which may be a risk to human health. Recently, many efforts have been allocated to develop secure and safe alternatives to antibiotics. On the other hand, the identity of molecules that modulate rumen fermentation to enhance the efficiency of feed conversion ratio is an important objective of ruminant nutrition research. The manipulation of the rumen microbial ecosystem to increase the efficiency of nutrients used by the animal has long been a goal for rumen microbiologists and nutritionists. Essential oils are aromatic oily fluids collected from plants, which can be used as natural additives in animal feeds because of their antibacterial, antifungal, and antioxidant aspects (Cowan 1999). The essential oils are volatile mixtures composed of secondary metabolites of plant material which are characterized by diverse compositions and activities (Benchaar et al. 2008). It is reported that many essential oils affect rumen fermentation (Hart et al. 2008) and they are currently being studied as rumen modifiers in ruminants. The antimicrobial effects of common essential oils extracted from medicinal plants have been proved, previously (Castillejos et al. 2006). Castillejos et al. (2005) showed that the addition of some essential oils into two different diets (high forage or high concentrate) in a continuous culture fermentation system during eight days increased TVFA concentration, but nitrogen metabolism did not differ. Therefore, the effect of using different levels of Lallemantia royleana essential oil (LREO) on some of the fermentative-microbial parameters, in vitro dry matter and organic matter degradability, gas production parameters, protozoa population, and methane emissions of a sheep's diet were investigated in an in vitro batch culture.
Material and methods: The whole samples of Balangu (Lallemantia royleana) were collected from the mountainous areas (Revenj village) of Torbat-e Jam at the flowering stage. The essential oil from whole parts of this plant was extracted by Clevenger's hydro-distillation apparatus. An in vitro batch culture was used to evaluate the effects of different levels of essential oil (0, 150, 300, and 450 mg/L) in the laboratory. The cumulative gas production at 3, 6, 9, 12, 24, 48, 72, and 96 h of incubation was measured and recorded. The in vitro dry matter (IVDMD) and organic matter (IVOMD) digestibilities were measured according to standard methods after 96 h of incubation. Some of the fermentative-microbial parameters [including pH, ammonia nitrogen, total volatile fatty acids (TVFA), microbial mass yield (MMY), partitioning factor (PF), and efficiency of microbial mass synthesis (EMMS)], methane emissions, and protozoa population were also determined in an in vitro batch culture similar to that used for gas production test according to standard methods.
Results and discussion: No changes were observed in the concentration of ammonia nitrogen and protozoal population of the culture medium due to the addition of LREO, but pH (linear, P=0.02) and TVFA significantly decreased and increased, respectively compared with the control group. With increasing LREO in the culture medium, most gas production parameters (potential gas production and gas production at 12, 24, 48, and 72 h of incubation) significantly increased as linear and quadratic; however, methane emissions did not change. Although IVDMDandIVOMD showed a significant increase (linear and quadratic) due to the addition of LREO; in contrast, the PF, MMY, and EMMS significantly decreased (linear and quadratic) compared with the control group. Supplementation of 5 mg/l of some essential oils increased by 8% the concentration of total VFA (Castillejos et al. 2007). Evans and Martin (2000) reported that thymol (400 mg/l) decreased the total VFA concentration, suggesting that the used dose was toxic to rumen bacteria. Previous studies (Molero et al. 2004 and Newbold et al. 2004) demonstrated that a blend of essential oils inhibited proteolysis and amino acid deamination. Recent studies showed that most essential oils tested at high concentrations (i.e., 3000 and 5000 mg/l) inhibited rumen microbial fermentation and reduced total VFA concentration, which demonstrates their antimicrobial activity (Cardozo et al. 2005, Busquet et al. 2006, Castillejos et al. 2006 ).
Conclusion: The overall results showed that LREO can alter the fermentation pattern in the medium by improving some of the parameters (increasing in gas yield, TVFA, IVDMD, and IVOMD), and it seems that the level of 450 mg of LREO/L has more effect on these parameters. The addition of LREO can also decrease the microbial mass yield in the rumen, modify the production of VFA without any change in ammonia nitrogen. Effects of LREO on in vivo rumen fermentation and animal performance require further researches.