This research was conducted in order to investigate the effects of Pistacia Atlantic subspecies Kurdica gum essential oil (PAKEO) on ruminal methanogen, protozoa, selected bacteria species, feed intake, and ruminal microbial fermentation in sheep. Six rumen-cannulated male Sanjabi sheep (average BW= 49 kg) were used in a crossover design with two periods and 2 treatments: control (CON, without additive) and PAKEO (1.2 ml/sheep/day of PAKEO). Voluntary feed intake and ruminal ammonia-N concentration were not affected, but ruminal pH was decreased by PAKEO. Total VFA concentration (P=0.06) and propionate molar proportion (P<0.05) increased, but acetate molar proportion was not affected in PAKEO treatment compared to the CON. Also, PAKEO supplementation decreased the acetate: propionate ratio (P= 0.05). Results showed that PAKEO supplementation increased (P < 0.01) the relative abundance of total bacteria and Ruminococcus flavefaciens, and decreased (P < 0.05) Fibrobacter succinogenes abundance, but did not influence Ruminococcus albus. The ruminal relative population of methanogens was dramatically decreased by PAKEO (P< 0.01). Protozoa population was not affected by adding PAKEO. Results suggest that PAKEO could have the potential as feed additives to change the rumen microbial population and subsequently improve the ruminal fermentation characteristics. The decrease in ruminal methanogens and enhanced production of the gluconeogenesis precursor, propionic acid, demonstrated that PAKEO could be used to improve ruminal fermentation.
