Laminaria digitata phlorotannins decrease protein degradation and methanogenesis during in vitro ruminal fermentation

Background: Phlorotannins (PhTs) are marine tannins consisting of phloroglucinol subunits connected via carbon-carbon and ether linkages. These have non-covalent protein binding properties and are, therefore, expected to be beneficial in protecting protein from hydrolysis during ruminal fermentation. In this study, the effectiveness of a methanolic PhTs extract from Laminaria digitata (10, 20, 40, 50, 75 and 100g kg-1 tannin-free grass silage, with or without addition of polyethylene glycol (PEG), was investigated in vitro on protection of dietary protein and reduction of methane (CH4) in ruminal fluid. Results: Addition of PhTs had linear (P<0.0001) and quadratic (P=0.0003) effects on gas and CH4 production, respectively. Optimal dosage of PhTs was 40g kg-1 as at this point CH4 decreased (P<0.0001) from 24.5 to 15.2mL g-1 organic matter (OM), without affecting gas production (P=0.3115) and total volatile fatty acids (P=1.000). Ammonia trended (P=0.0903) to decrease from 0.49 to 0.39mmol g-1 OM, indicating protection of protein. Addition of PEG inhibited the effect of tannins at all dosage levels, and none of the fermentation parameters differed from the control. Conclusion: PhTs effectively protected protein from fermentation and reduced ruminal methanogenesis.