Production of N 2 and N 2 O from nitrate ingested by sheep

• Published in: Journal of animal physiology and animal nutrition 2018-02, Vol.102 (1), p.e176
• Main Authors: de Raphélis-Soissan, V, Nolan, J V, Godwin, I R, Newbold, J R, Eyre, B D, Erler, D V, Hegarty, R S
• Format: Article
• Language: English
• Subjects: Animals; Diet - veterinary; Nitrates - administration & dosage; Nitrates - metabolism; Nitrogen - metabolism; Nitrogen Isotopes; Nitrous Oxide - metabolism; Sheep - metabolism
• ISSN: 0931-2439; 1439-0396
• DOI: 10.1111/jpn.12725

Supplementing ruminants with nitrate (NO3-) reduces their enteric methane (CH ) emissions; however, the greenhouse gas (GHG) mitigation achieved can be partially offset by small emissions of nitrous oxide (N O), a more potent GHG. Sheep were dosed intraruminally with NO3- to investigate whether dietary NO3- is a precursor of N O and/or di-nitrogen gas (N ), and to quantify the amounts of NO3- recovered as N O and N in gas emissions from sheep adapted or not adapted to dietary NO3-. Ruminally cannulated sheep were adapted to a hay diet supplemented with NO3- (n = 3; 10 g NO3-/kg DM) or urea (n = 3; 5.3 g urea/kg DM). On the day of the experiment all sheep were dosed intraruminally with NO3- and quickly moved into gas-tight chambers to enable recovery of N in N O and N to be measured. Measurements of gases accumulating in the chambers were made over 10 successive 50 min periods; this enabled the amount of N O produced, and the recovery of NO3--N in N O and N to be determined over a total of 10 hr. Only 0.04% of labelled NO3--N was recovered as N O, and this was not dependent (p > .05) on whether or not the animals had been adapted to dietary NO3-. Approximatively 3% of NO3--N was recovered as N , which was also not dependent (p > .05) on whether sheep had been adapted to NO3-. Because the kinetics of rumen ammonia (NH ) were uncertain, the recovery of N from NO3- in rumen NH could not accurately be quantified, but our results suggest that approximately 76% of dietary NO3- was converted to NH in the rumen. We conclude that the small amount of NO3- recovered in N was evidence of denitrification, previously thought not to occur in the rumen.