Nitrate as fermentable nitrogen supplement to reduce rumen methane production

Abstract

Three rumen-fistulated cattle were allocated to a 3 x 3 Latin square to compare sodium nitrate (SN), ammonium nitrate (AN) and urea (U) as sources of fermentable nitrogen in a basal diet of NaOH-treated rice straw and cottonseed meal. The diets were iso-nitrogenous with levels of sodium nitrate, ammonium nitrate and urea of 6.6, 3.0 and 2.2% in DM, for SN, AM and U, respectively. Experimental periods were 4 weeks, the first two weeks for adaptation to increasing levels of the N source, and the second two weeks at the required level of the N source. Feces were collected during the final 7 days of each period. Samples of rumen fluid were taken on the last day of each period. The same treatments were compared in an in vitro experiment with 3 repetitions in a completely randomized design. The forage components of the diets were dried and milled through a 1 mm screen and mixed with the other components of the diet. Representative samples (20 g DM) were put in an incubation flask (2500ml) to which were added 1.6 liters of buffer solution and 400ml of rumen fluid, prior to filling each flask with carbon dioxide. The rumen fluid for each treatment was obtained from the rumen-fistulated cattle that were on the same dietary treatments. The flasks were then incubated at 38 0 C in a water bath for 72h. During the incubation, each flask was connected to an aluminium bag for total collection of gas over the 72h period. At the end of the incubation the total gas volume was recorded and samples analyzed for the proportions of methane and carbon dioxide. There were no differences among treatments in feed intake, apparent DM digestibility and live weight change of the cattle. Rumen ammonia after feeding was higher in rumen fluid from cattle fed nitrate compared with those fed urea. Concentrations of acetate were higher on the nitrate diets. In the in vitro experiment, methane concentration in the gas, and the methane: carbon dioxide ratios, were lower when sodium nitrate or ammonium nitrate were the sources of fermentable N compared with urea.