Dose-response effects of Asparagopsis taxiformis and Oedogonium sp. on in vitro fermentation and methane production

This study aimed to identify the optimal doses of the macroalgae Asparagopsis taxiformis and Oedogonium sp., individually and in combination, which would decrease the in vitro production of methane while minimizing adverse ef- fects on fermentation, using rumen inoculant from Bos indicus steers. The dose-response experiment evaluated ten doses of Asparagopsis [ranging from 0 to 16.7 % of the organic matter (OM) incubated] and seven doses of Oedogonium (ranging from 0 to 100 % OM) using Rhodes grass hay as a basal substrate. Asparagopsis was highly effective in decreasing the production of methane with a reduction of 99 % at doses aslowas2%OMbasis.However,adoseof2%OMalso decreased the production of volatile fatty acids (VFA). Oedogonium was less effective with doses ≥50 % OM signif- icantly decreasing the production of methane. A combination of Asparagopsis (2 % OM) and Oedogonium (25 and 50 % OM) continued to suppress the production of methane, inde- pendent of the inclusion rate of Oedogonium. The effective- ness of Asparagopsis demonstrates its potential for the miti- gation of methane emissions from ruminants at inclusion rates of ≤2 % OM. Oedogonium is a potential feed supplement due to its nutritional value, but supplements ≤25 % OM are recommended to avoid adverse effects on apparent in vitro fermentation.