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1607
Effect of nitrate, monensin and the combination of additives on rumen fermentation using a semi-continuous culture system
A 37-d experiment was conducted to investigate the effect of nitrate (NIT) and monensin (MON) on rumen fermentation using a semi-continuous culture system. We hypothesized that the combination of additives would reduce CH4 emissions beyond that of either additive alone, without affecting production parameters. Additives (0, 1.25 and 2.5% diet DM of NIT; 0 and 4 mg/L of MON) were tested alone and in combination (NIT + MON; 6 total treatments; 3 replicates per treatment). Buffer and water were added to 18, 2.2-L vessels on d -8 (1.2 L of a 50:50 mixture). The first 7 d (d -7 to d 0) served as a steady-state phase. On d -7, rumen fluid was pooled from 5 non-adapted lactating cows fed a 50:50 forage to concentrate diet, filtered through 2 layers of cheesecloth, and 1 L was transferred to each vessel along with 30 g of solid rumen content and 20 g of a basal diet (50:50 forage to concentrate) in a 8 × 20 cm nylon bag (50 µm mesh size). On d -6, 20 g of the basal diet replaced the solid rumen content bag, and from this point onward 2 bags, each containing 20 g of the treatment diet, were always present in the vessels for 48 h. Buffer was infused at a constant rate (70 ml/h) throughout the experiment with a peristaltic pump. Gas production was measured daily. Twice weekly dry matter disappearance (DMD), pH and ammonia nitrogen (NH3-N) were measured. Treatment did not affect DMD (69.13 g/100g DM; P>0.05). Compared to the negative control treatment, addition of NIT reduced total gas production (2.84 vs. 3.03 L/d; P=0.02), CH4 production (28.65 vs 40.9 mM/d; P<0.01) and CO2 production (87.57 vs. 97.36 mM/d P<0.05). Compared to the negative control, addition of MON reduced CH4 production (29.4; P<0.01). Further CH4 reduction, compared to the negative control, was observed when NIT+MON was added (24.31 vs 40.9 mM; P=0.04). No treatment effects were observed for pH (7.1) or protozoa count (4.3 x103). Addition of NIT reduced NH3-N (16.65 vs 23.5 mg/dL; P<0.01). The combination of NIT+MON enhanced reduction of CH4 production in a semi-continuous culture fed 50:50 forage to concentrate diet, with no detriment to DMD.
Keywords: Methane, in vitro, protozoa