The Action Potential of Antioxidant Grape Seed Proanthocyanidin as a Rumen Modifier to Mitigate Rumen Methanogenesis In Vitro.

Grape seed proanthocyanidin (GSP) contains polyphenolic bioflavonoids ubiquitously found in the lignified portions of grape seeds from the winery and distillery industries, as an antioxidant. To explore its potential as a rumen modifier in methanogenesis inhibition, a 2 × 5 factorial experiment was conducted to determine the effect of GSP at 0, 15, 30, 60 and 120 mg/g of substrate on the rumen fermentation and methanogenesis of two representative total mixed rations (HY, a diet for high-yield (>2 kg/d) lactating cows, and LY, a diet for low-yield (<25 kg/d) lactating cows). By using the MIXED procedure, after a 48 h in vitro rumen incubation, increasing the GSP addition linearly decreased the in vitro dry matter digestion (IVDMD) and slowed down the rates of ration fermentation (RmaxS, g/h) and kinetic gas production (RmaxG, mL/h), with the decreases being more pronounced in the LY than HY group (p < 0.05). The GSP addition decreased hydrogen recovery (2Hrec) and altered the fermentation gas composition. The molar CH₄ proportion was significantly reduced with both 60 and 120 mg GSP addition (p < 0.01). The total volatile fatty acid production was linearly decreased with the increasing GSP addition (p < 0.01). In addition, the GSP addition significantly decreased the ratio of methanogens to total bacteria (p < 0.05), and the reduction was notably greater in the HY than in the LY substrate (45.3% vs. 15.2% decrease), although the diversity of rumen methanogenic archaea was not affected in either the HY or the LY group. Bioinformatic analysis illustrated that the rumen archaeal community was predominated by a Methanobrevibacter genus (>72.5%), followed by Methanomassiliicoccus (>20.9%) and Methanosphaera (>1.0%). Methanobrevibacter could play an important role in methanogenesis in the presence of GSP, though it is usually considered to be the main hydrogenotrophic methanogen. In brief, the GSP addition presented high potential as a rumen modifier to mitigate methanogenesis by decreasing the ratio of methanogens to total bacteria. Methanobrevibacter could play an important role in methanogenesis in the presence of GSP. However, a relatively low administration level of GSP should be taken into consideration in order to obtain its inhibitory effect on CH₄ emission, with a minimal negative effect on rumen digestion and fermentation. [ABSTRACT FROM AUTHOR]