Effects of the Appropriate Addition of Antioxidants from Pinus densiflora and Mentha canadensis Extracts on Methane Emission and Rumen Fermentation

SIMPLE SUMMARY: In the livestock industry, increasing attention is being focused on ways to reduce artificial greenhouse gas emissions from ruminants or provide alternatives to homeostasis. Pinus densiflora and Mentha canadensis extracts, with antioxidant properties, inhibit methanogenesis in ruminants and improve both digestion and growth of animals. Long-term stability of these plant extracts provides further support for their use as a substitute for other rumen regulators. It is expected that new additives for ruminants will be developed from P. densiflora and M. canadensis extracts, which are composed of phenolic compounds for improving the growth and immunity of ruminants. ABSTRACT: This study aimed to investigate the optimal addition of terpene-based Pinus densiflora and Mentha canadensis extracts, with antioxidant and methane reduction effects, as feed supplements to ruminants. Two cannulated steers (450 ± 30 kg), consuming Timothy Hay and a commercial concentrate (60:40, w/w) twice daily (at 09:00 and 17:30) at 2% of body weight, with free access to water and a mineral block, were used as rumen fluid donors. In vitro fermentation experiments, with Timothy Hay as the substrate, were conducted with P. densiflora and M. canadensis extracts as supplements to achieve concentrations of 30, 50, and 70 mg/L on a Timothy Hay basis. Fibrobacter succinogenes decreased in proportion upon P. densiflora and M. canadensis extract supplementation at 50 mg/L, while the dry matter degradability of the feed was not significantly different (p < 0.05). Methane emission was significantly lower in the 50 and 70 mg/L treatment groups, for both extracts, at 12 h (p < 0.05). Based on methane production and antioxidant activity, our study suggests that 30 mg/L addition is the most appropriate level of supplementation.