gas emission from waste of cows fed monensin and acacia mearnsii tannins

The study aimed to evaluate the effect of combined use of tannins and monensin on biogas production from waste of nellore cows fed these additives through biodigesters as a way to improve animal waste manage-ment. eight cows were arranged in 2 contemporary 4 × 4 latin squares design and received 8 diets that dif-fered in the level of tannin inclusion (0.00, 0.75, 1.50, and 2.25% dm) and inclusion or not of monensin. monensin was daily administered to each cow in one square (32 mg/kg dm). faeces and urine were col-lected for anaerobic biodigestion. experimental batch-type biodigesters were arranged in a completely ran-domised design, in a 2 × 4 factorial arrangement of 8 treatments with 4 replicates. the data were submitted to statistical analysis system. monensin did not affect total biogas production (p>0.05) but reduced co2 production by 18.90%. tannins had a quadratic effect on total solids (ts) biodigestion efficiency, but bio-digestion efficiency for volatile solids (vs) and nitrogen linearly reduced (p<0.05). tannins had a quadratic effect on total biogas and ch4 production (at 2.25% the total biogas and ch4 production reduced by 36.95 and 36.10%, respectively) and linearly reduced the production of co2 (p<0.05). antagonistic interactions between monensin and tannins were observed on ts and vs recovery and vs biodigestion efficiency, where monensin reduced the effect of tannins of reducing the vs or ts biodigestion. therefore, monensin and tannins may be used to reduce the emission of greenhouse gases from cattle waste when tannins are included above 0.75%. there is a strong evidence that monensin and tannins or their bioactive metabolites may appear in faeces (when used to feed cows) and impair the biodigestion of the waste, but further studies should be carried out to confirm this finding.