I have no problems with the science but I think the MS needs quite a bit of editing in order to present the findings accurately. A lot of the issues are cosmetic (i.e. the reference style changes from the Introduction to the Discussion; abbreviations are inconsistent/repeated).

There are also some science editing required. For example (not the only example) there is a sentence in the Results and Discussion which states: "The lowest CH4 production was from manure collected from steers fed with a 0.3% tannin supplement (79.00 NL kg?1 VS). BMP was significantly lower for manure collected from steers receiving 0.4 and 0.5% tannin than for manures from steers receiving control diets (respectively 90.95 and 91.23 NL kg?1 VS). It is known that tannins in feed given to livestock reduces feed digestibility [20], and that tannins are slowly digested by the livestock and consequently are excreted in manures. This study shows that tannin in the manure inhibits the fermentation of manure organic matter, and results in reduced CH4 production. It is known that tannins may also inhibit microbial activity"

Table 3 shows that 0.3% is different from the control but 0.4 and 0.5% are not in terms of CH4 production - which is inconsistent with the statement above. However, all three are different from the control in terms of Biogas production - there is much discussion which could be teased out and the MS would benefit from a couple of hours rigorous scientific editing.