Effect of tannins-rich extract from Acacia mearnsii or monensin as feed additives on ruminal fermentation efficiency in cattle

Methane, a powerful greenhouse gas, is considered to be a significant loss of productive potential in ruminants. The objective was to evaluate the effect of monensin and Acacia mearnsii tannins on ruminal fermentation efficiency in cattle. Six rumen-cannulated cows were distributed three diets, each of which differed in the additive used, in a replicated 3×3 Latin square experimental design. Treatments were the Control, Monensin (300 mg per animal and day or about 18 mg/kg of dry matter - DM) and a tannin-rich extract from Acacia mearnsii (100 g per animal and day or about 0.6% of DM). Each experimental period consisted of 21 days; the first 15 days were used for diet adaptation and the last 5 days for data collection. On experimental day 21, ruminal pH was analyzed by a continuous measurement probe. In order to quantify short-chain fatty acids (SCFA), methane (CH4), NH3-N (ammonia nitrogen) production, protozoa and the ruminal dynamics, rumen contents were sampled prior to and 3, 6, 9 and 12 h after morning feeding. The fermentation technique consisted of incubation of liquid and solid rumen contents in bottles in a water bath (39 °C) for 30 min. Subsequent measurement of methane production was made using gas chromatography and used for the final estimation of Relative Energy Loss (REL). There was no effect (P>0.05) of additives on pH, ruminal DM disappearance rate, the concentrations of NH3-N, the production of acetic or butyric acids or the total ruminal SCFA. Monensin treatment was responsible for reducing CH4 production by 10.7%, whereas tannin inclusion reduced it by 8.0%, when compared to the control treatment. The REL was decreased (P<0.05) by 20.3% and 23.8% with tannin and monensin administration, respectively. Additionally, monensin increased propionic acid production by 39.5% when compared to the control treatment (P<0.05); therefore, the short-term use monensin or tannin in diets with the same proportion of roughage and concentrate has shown to be a viable option when formulating cattle diets aimed at improving energy efficiency.