Four Hu sheep (27.5. ±. 2.6. kg body weight), fitted with ruminal and duodenal fistula, were used to investigate the effects of a mixture of essential oils (EO) or their active components on rumen fermentation, microbial population, and nutrient digestibility. Four treatments in 4. ×. 4 Latin square design were used: basal diet added with 25. g/day monosodium fumarate (Control); Control plus 1. g/day of EO combinations (EOC, mixture of equal ratio of oil from clove, oregano, cinnamon, and lemon); and Control plus 0.5 or 1.0. g/day EO active component combinations (EOAC, mixture of eugenol, carvacrol, citral and cinnamaldehyde in equal ratio). The EOC and EOAC treatments were absorbed into microporous starch, and the complex was encapsulated with sodium alginate before use. Each treatment period lasted for 21 days, including 12 days for adaptation. Rumen samples were taken to determine volatile fatty acid (VFA) content and microbial flora. Microbial populations were measured using real-time PCR. The apparent digestibility of nutrients in the total tracts or at different tract parts was measured through total collection method or indicator method, respectively. Rumen pH did not change with the addition of EOC or EOAC. Ammonia nitrogen concentration decreased after addition of either EOC or EOAC. Total VFA content decreased with the addition of EOC or high level of EOAC, with little change under low dose of EOAC. Propionate increased (P<0.05) in animals treated with EOAC or 0.5. g EOAC compared with the control. The ratio of acetate to propionate decreased (P<0.05) with the addition of EOC or EOAC. Protozoan population decreased (P<0.05) with the addition EOC and EOAC, with lower population in the EOAC-treated animals than in the EOC-treated group. The growth of methanogens, Fibrobacter succinogenes, and Butyrivibrio fibrisolvens (P<0.05) was inhibited by addition of EOAC, but not by EOC. Population of fungi and Ruminococcus flavefaciens did not change with the addition of EOC or EOAC. Addition of EOC and EOAC did not influence the feed intake and digestibility of the nutrients in total or at different parts of the digestive tract, but decreased ruminal protein digestibility. Addition of EOC and EOAC has no obvious harmful effects on rumen fermentation in terms of ruminal dry matter and fiber digestibility was not influenced. The proportion of ruminal propionate increased, and protein degradation was inhibited. In this study, the addition of 1. g/day EOC or EOAC had no detrimental effects on sheep nutrient digestion. © 2013 Published by Elsevier B.V.
