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 x 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 degrees 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.