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Production of N 2 and N 2 O from nitrate ingested by sheep
Author(s) -
de RaphélisSoissan V.,
Nolan J. V.,
Godwin I. R.,
Newbold J. R.,
Eyre B. D.,
Erler D. V.,
Hegarty R. S.
Publication year - 2018
Publication title -
journal of animal physiology and animal nutrition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.651
H-Index - 56
eISSN - 1439-0396
pISSN - 0931-2439
DOI - 10.1111/jpn.12725
Subject(s) - rumen , nitrous oxide , zoology , urea , hay , nitrate , chemistry , nitrogen , greenhouse gas , methane , biology , food science , fermentation , biochemistry , ecology , organic chemistry
Summary Supplementing ruminants with nitrate ( NO 3 − ) reduces their enteric methane ( CH 4 ) emissions; however, the greenhouse gas ( GHG ) mitigation achieved can be partially offset by small emissions of nitrous oxide (N 2 O), a more potent GHG . Sheep were dosed intraruminally with 15 NO 3 − to investigate whether dietary NO 3 − is a precursor of N 2 O and/or di‐nitrogen gas (N 2 ), and to quantify the amounts of NO 3 − recovered as N 2 O and N 2 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 N 2 O and N 2 to be measured. Measurements of gases accumulating in the chambers were made over 10 successive 50 min periods; this enabled the amount of N 2 O produced, and the recovery of 15 NO 3 − ‐N in N 2 O and N 2 to be determined over a total of 10 hr. Only 0.04% of labelled NO 3 − ‐N was recovered as N 2 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 N 2 , which was also not dependent ( p > .05) on whether sheep had been adapted to NO 3 − . Because the kinetics of rumen ammonia ( NH 3 ) were uncertain, the recovery of 15 N from NO 3 − in rumen NH 3 could not accurately be quantified, but our results suggest that approximately 76% of dietary NO 3 − was converted to NH 3 in the rumen. We conclude that the small amount of NO 3 − recovered in N 2 was evidence of denitrification, previously thought not to occur in the rumen.