Production of N2 and N2O from nitrate ingested by sheep. Issue 1 (12th June 2017)

• Record Type: Journal Article
• Authors: de Raphélis‐Soissan, V.; Nolan, J. V.; Godwin, I. R.; Newbold, J. R.; Eyre, B. D.; Erler, D. V.; Hegarty, R. S.
• Is Part Of: Journal of animal physiology and animal nutrition. Volume 102:Issue 1(2018)
• Page Start: e176
• Page End: e182
• Publication Date: 2017-06-12
• Subjects: denitrification -- methane -- nitrogen -- nitrous oxide -- ruminant; Animal nutrition -- Periodicals; Feeds -- Periodicals; 636.085
• DOI: 10.1111/jpn.12725
• Languages: English
• ISSNs: 0931-2439

Abstract

Summary: Supplementing ruminants with nitrate ( NO 3 − ) reduces their enteric methane (CH4 ) emissions; however, the greenhouse gas (GHG) mitigation achieved can be partially offset by small emissions of nitrous oxide (N2 O), a more potent GHG. Sheep were dosed intraruminally with 15 NO 3 − to investigate whether dietary NO 3 − is a precursor of N2 O and/or di‐nitrogen gas (N2 ), and to quantify the amounts of NO 3 − recovered as N2 O and N2 in gas emissions from sheep adapted or not adapted to dietary NO 3 − . Ruminally cannulated sheep were adapted to a hay diet supplemented with NO 3 − ( n = 3; 10 g NO 3 − /kg DM) or urea ( n = 3; 5.3 g urea/kg DM). On the day of the experiment all sheep were dosed intraruminally with 15 NO 3 − and quickly moved into gas‐tight chambers to enable recovery of 15 N in N2 O and N2 to be measured. Measurements of gases accumulating in the chambers were made over 10 successive 50 min periods; this enabled the amount of N2 O produced, and the recovery of 15 NO 3 − ‐N in N2 O and N2 to be determined over a total of 10 hr. Only 0.04% of labelled NO 3 − ‐N was recovered as N2 O, and this was not dependent ( p > .05) on whether or not the animals had been adapted to dietary NO 3 − . Approximatively 3% of 15 NO 3 − ‐N was recovered as 15 N2, which was also not dependent ( p > .05) on whether sheep had been adapted to NO 3 − . Because the kinetics of rumen ammonia (NH3 ) were uncertain, the recovery of 15 N from NO 3 − in rumen NH3 could not accurately be quantified, but our results suggest that approximately 76% of dietary NO 3 − was converted to NH3 in the rumen. We conclude that the small amount of NO 3 − recovered in N2 was evidence of denitrification, previously thought not to occur in the rumen.