Effects of nitrate sources on in vitro methane production and ruminal fermentation parameters in diets differing in starch degradability

We evaluated the effects of nitrate (NO3−) sources supplemented in diets differing in starch degradability on in vitro DM and NDF degradability, methane (CH4) and nitrous oxide (N2O) production, and ruminal fermentation parameters. The experiment followed a randomized complete block design with a 5 × 2 factorial arrangement. Treatments were five sources of non-protein nitrogen (NPN), including urea (URE), potassium NO3− (PON), calcium-ammonium NO3− (CAN), dolomite-ammonium NO3− (DAN), and ammonium NO3− (AMN), supplemented on total-mixed rations constituted with either high-moisture corn (HMC) or dry rolled corn (DRC). In vitro DM and NDF degradability, gas production, CH4 and N2O emissions, and VFA and ammonia-N concentrations were evaluated after 12 and 24 h of incubation. All experimental procedures were repeated in three runs and run was used as a blocking factor. In vitro DM and NDF degradability were not affected by NO3− sources. Nitrate supplementation decreased CH4 production (mmol/ g DM degraded) by 23 % compared to URE regardless of the source. Concomitantly, N2O emissions were increased by all NO3− sources, with the highest amount (1.24 ppm) for PON after 24 h of incubation. High-moisture corn diets improved in vitro DM and NDF degradability, increased propionate production, and consequently reduced acetate: propionate ratio. Methane production (mmol/g DM degraded) was reduced by 34 % in HMC diets after 24 h of incubation when compared with DRC diets. No interactions were observed between NO3− and starch sources in all the evaluated parameters, leading us to conclude that NO3− sources acted independently at reducing CH4 production, regardless of the rate of ruminal starch degradation.