Nitrate (NO3-) supplementation is a promising methane mitigation strategy for ruminants, but can cause nitrite (NO2-) poisoning. Because some nitrite reductases are NADH-dependent, we hypothesised that replacing glucose with glycerol would increase the NADH yield and so enhance nitrite reductase activity and reduce ruminal NO2- accumulation and toxicity risk. We also hypothesised that adapting sheep to dietary NO3- would limit the accumulation of NO2- when NO3- was added to rumen fluid. Changes in NO3- and NO2- catabolism and CH4 production, resulting from supplementation with glycerol to enhance NADH supply, were studied in vitro. In Experiment 1, rumen fluid from sheep adapted to dietary NO3- (2% of DM intake) or urea (1.1% of DM intake) was incubated with NO3- or urea, respectively. Additionally, ground oaten hay was added to incubations alone (control), or with glucose or glycerol. In Experiement 2, sheep were adapted for 9 weeks to dietary NO3- or urea. Nitrate (2% NO3- of substrate DM) was added to incubated digesta from NO3-or urea-supplemented sheep, while urea (1.1% of substrate DM) was added to digesta from urea-supplemented sheep. In both studies, triplicate incubations were terminated at nine time points up to 24 h. Methane emissions were lower in all NO3- treatments (P < 0.05). Contrary to our hypotheses, both glycerol supplementation (Experiment 1) and prior adaptation to NO3- (Experiment 2) increased NO2- accumulation. In Experiment 1, there was no difference in ruminal NO2- concentration between the unsupplemented control and added glucose treatments. Nitrous oxide accumulated in NO3- treatments only with rumen fluid from sheep adapted to dietary urea (P < 0.05). In summary, NO2- accumulation in vitro was not reduced by adaptation to NO3- or by glucose or glycerol supplementation, disproving the hypotheses regarding the role of NADH availability and of NO2- adaptation in reducing ruminal NO2- accumulation and toxicity risk.
|Number of pages||8|
|Journal||Animal Production Science|
|Early online date||9 Feb 2016|
|Publication status||First published - 9 Feb 2016|
- fermentable carbohydrate
- greenhouse gases
- nitrite poisoning.