Evaluation of origanum oil, hydrolysable tannins and tea saponin in mitigating ruminant methane: In vitro and in vivo methods

The objective of this study was to investigate the effects of origanum oil (ORO), hydrolysable tannins (HYT) and tea saponin (TES) on methane (CH(4)) emission, rumen fermentation, productive performance and gas exchange in sheep by using in vitro and in vivo methods. The ORO, HYT and TES additive levels were normalized per kg dry matter (DM) in both in vitro and in vivo experiments: ORO‐0, 10, 20 and 40 ml/kg; HYT‐0, 15, 30 and 60 g/kg; and TES‐0, 15, 30 and 60 g/kg, respectively. During in vitro incubation, 40 ml/kg ORO linearly decreased CH(4) emission (p < 0.05); 20 and 40 ml/kg ORO cubically decreased carbon dioxide (CO(2)) production (p < 0.05), and rumen pH was cubically raised with the increasing ORO additive level (p < 0.01). The 60 g/kg HYT cubically decreased CH(4) production (p < 0.05). The pH of 60 g/kg HYT was higher than that of 15 and 30 g/kg (p < 0.01); the pH of 20 g/kg TES was higher than that of 5 g/kg (p < 0.05). In the in vivo experiments, 40 ml/kg ORO inhibited dry matter intake (p < 0.01) cubically and reduced average daily gain (ADG) and feed conversion ratio (FCR) cubically (p < 0.05), and 20 or 40 ml/kg ORO linearly decreased CH(4) production based on per day or metabolic weight (W(0.75)) (p < 0.05). Both 30 and 60 g/kg HYT linearly inhibited CH(4) emission on the bases of per day and W(0.75) (p < 0.05). The 20 g/kg TES improved the apparent digestibility of crude protein (p < 0.05), 10 and 20 g/kg of TES decreased CH(4) emission (p < 0.05), and 5 g/kg of TES reduced O(2) consumption and CO(2) production (p < 0.05). In conclusion, these three plant extracts all showed the abilities on mitigating CH(4) emission of sheep with appropriate additive ranges.