Effects of Perovskia abrotanoides Kar. Essential Oil on Greenhouse Gas Mitigation and Energy Efficiency Improvement in Sheep Rumen: An In Vitro Study.

Abstract

Background: The use of natural additives in animal nutrition, particularly for ruminants, has gained attention due to environmental concerns and the need to improve rumen fermentation efficiency. Essential oils are bioactive sources that can modulate rumen microbes and reduce methane production, a major greenhouse gas and source of energy loss.

Objectives: This study aimed to characterize the chemical composition of Perovskia abrotanoides Kar. essential oil and evaluate its potential as a natural rumen modifier by assessing its effects on in vitro rumen fermentation parameters, gas and methane production, protozoa population, nutrient degradability and microbial efficiency.

Methods: Essential oil was extracted by water distillation and analysed using GC/MS. Rumen fluid was collected from three fistulated sheep that fed a maintenance diet. Six levels of essential oil (0, 100, 200, 300, 400 and 500 mg/L culture medium) were evaluated in a completely randomized design. Gas production was measured at 0-96 h, whereas methane, volatile fatty acids (VFAs), ammonia nitrogen (NH₃-N), pH, protozoa count, degradability and microbial parameters were measured after 24 h. Data were analysed using ANOVA followed by Tukey's multiple comparison test.

Results: GC/MS analysis revealed 33 compounds, with 1,8-cineole (16.1%), camphor (13.8%), α-pinene (8.4%) and δ-3-carene (6.8%) as the predominant constituents. Increasing concentrations of P. abrotanoides essential oil produced dose-dependent changes in rumen fermentation. The highest supplementation level (500 mg/L) led to the most significant reductions in methane production (58%), total protozoal population, total VFA concentration, NH₃-N concentration and the degradability of dry matter, organic matter and neutral detergent fibre, while simultaneously producing the highest ruminal pH, microbial biomass production, microbial synthesis efficiency and partitioning factor (p < 0.0001). In contrast, supplementation at 200-300 mg/L maintained a more favourable balance between methane mitigation and nutrient degradability.

Conclusions: The findings demonstrate that P. abrotanoides essential oil, rich in oxygenated monoterpenes, such as 1,8-cineole and camphor, effectively reduced methane production and protozoa population while improving microbial efficiency under in vitro conditions. The greatest reduction in methane production and in protozoal population was observed at 500 mg/L, whereas supplementation at 200-300 mg/L provided the best balance between methane mitigation and maintenance of rumen fermentation efficiency. These results suggest that this essential oil could serve as a promising natural feed additive for mitigating enteric methane emissions and improving energy utilization in ruminants. Further in vivo studies are recommended to confirm these effects under practical feeding conditions.