The effect of Nepeta glomerulosa Boiss. (Lamiaceae) essential oil (NGEO) on in vitro gas production and ruminal fermentation

The study aimed to evaluate the chemical composition and the effects of Nepeta glomerulosa Boiss. (Lamiaceae) essential oil (NGEO) on in vitro gas production and ruminal fermentation. The essential oil (EO), obtained by steam distillation from Nepeta glomerulosa Boiss. (0, 150, 300, and 450 mg/L), was investigated in an in vitro culture medium using sheep rumen fluid and artificial saliva. A fattening diet was used as the substrate in the culture medium and gas production was measured. The profile of NGEO was determined by GC-mass analysis. The 1, 8-cineole (23.2%), α-pinene (15.3%), limonene (9.1%), and β-pinene (3.5%) were the major components in NGEO. Ammonia nitrogen and total volatile fatty acids (TVFA) concentrations did not change when NGEO was added to the culture medium, whereas TVFA tended to increase at the higher concentration of NGEO (P<0.1). The pH value of the culture medium linearly and quadratically decreased with increasing NGEO (P<0.05). The potential of gas production (bgas; linear, and quadratic, P<0.05) increased with increasing NGEO, however, the constant rate decreased linearly and quadratically (P<0.05). Dry matter (DMD) and organic matter degradability (OMD) were increased (linear and quadratic) with increasing NGEO in the culture medium. The partitioning factor (PF), microbial mass yield (MMY), and efficiency of microbial mass synthesis (EMMS) linearly and quadratically decreased when the concentration of NGEO increased. It seems that NGEO affected the fermentation process in vitro partly via improving TVFA production or by increasing DMD and OMD. Further in vitro and in vivo studies are needed to confirm that NGEO in the diet has no adverse effects on the health and production in ruminants.