Rumen methane abatement by phlorotannin derivatives (phlorofucofuroeckol-A, dieckol, and 8,8 '-bieckol) and its relationship with the hydroxyl group and ether linkage

Brown algae supplementation is one method for lowering rumen CH4 production because of the ability of the brown algae's phlorotannins to mitigate enteric CH4 emissions. The objective of this study was to evaluate the effects of phlorotannin derivatives, phlorofucofuroeckol-A (PFFA), dieckol (DE), and 8,8 '-bieckol (BE), on rumen in vitro CH4 emissions and to investigate the relationship between the number of their hydroxyl groups or ether linkages with CH4 reduction rate of phlorotannin derivatives. Rumen fluid obtained from two cannulated Holstein cows were incubated in an in vitro batch culture system for 24 and 48 h. Each phlorotannin derivative was added to the substrate at the five different concentrations of 0, 2, 4, 8, and 16 g/kg on a dry matter basis. Methane emission was decreased by 16 g/kg PFFA (linear, P < .01; quadratic, P = 0.06) and DE (linear, P < .01) supplementation and by 8 g/kg BE (linear, P < .01; quadratic, P = 0.05) addition at 24 h of incubation. There were no differences in rumen CH4 production at 48 h of fermentation. Total gas production was decreased at 24 h of incubation by PFFA (linear, P < .01; quadratic, P < .01), DE (linear, P < .01), and BE (linear, P < .01; quadratic, P = 0.02). The model for total gas production and CH4 emissions upon PFFA (r2 = 0.69, P < .01, and r2 = 0.65, P < .01, respectively) and BE supplementation (r2 = 0.42, P = 0.04, and r2 = 0.71, P < .01, respectively) showed a quadratic correlation. The CH4 abatement rate was positively correlated with the number of hydroxyl groups and ether linkages of phlorotannin derivatives (r2 = 0.46, P < .01, and r2 = 0.32, P < .01, respectively). In conclusion, the three pure and individual phlorotannin derivatives (PFFA, DE, and BE) in brown algae are candidates for rumen CH4 abatement, and their CH4 mitigating effects could depend on the number of the hydroxyl groups and ether linkages.