Sheep- Feed Methanogenic Inhibitors

Feed Methanogenic Inhibitors

System: Sheep

Mainly applicable for: Semi-intensive/intensive systems (with compound feed and premixes); slow-release/alternative delivery in extensive systems.

Not applicable or effective for: Low-input production systems, or pastoral systems, unless a slow-release form of nitrate is supplemented or an alternative route ensuring frequent feeding of nitrate becomes operational .

Description

Inclusion of methanogenic inhibitors in sheep diets in order to reduce the enteric methane emission in the rumen. Currently only nitrate is listed as methanogenic inhibitor below. 3-Nitrooxypropanol (3-NOP) is also effective in sheep, but not registered yet for sheep. For more information on 3-NOP, see factsheets for dairy and beef systems.

Supplementation of nitrate should follow the recommended dose and an adaptation phase for the sheep rumen to get adapted to the presence of nitrate by gradual increase of dose to the target level. ‘Slow release’ formulations may be used in grazing systems on farms that do not have in-shed feeding systems.

Mechanism of effect

Supplemented nitrate reduces enteric methane emission mainly by acting as a hydrogen sink when it is reduced to ammonia by rumen micro-organisms, leaving less hydrogen substrate for methanogens. To a smaller extent it also acts as an enzyme-inhibitor for methanogens. The specific mode of action is the same across animal species but its efficacy differs due to different conditions in the rumen environment. As nitrogen is added to the ration, ammonia and nitrous oxide emissions from manure storage and application may increase if the ration is not optimized accordingly.

Reference situation

Not feeding a diet with substantial content of nitrate (e.g., in recently, or strongly fertilized pastures in a young stage of (re)growth)

Legend

● – Small effect (<5%)	o – No effect
●● – Medium effect (5-20%)	● – Unfavourable effect
●●● – Large effect (>20%)	● – ● – Variable effect (depending on farm characteristics or way/level of implementation)

Effect on total greenhouse gas (GHG) emissions (LCA)

Mean effect and range in kg CO2-equivalents	per kg product		per farm
	Mean	Min-Max	Mean	Min-Max	Level of evidence
Nitrate	●●	● – ●●	●●	●–●●	Medium

Effect per emission source

Mean effect on emission from	Manure		Animal	Feed and forage production			Barn & farm inputs
	CH₄	N₂O	CH₄	CO₂	N₂O	LUC	CO₂
Nitrate		●	●●		●		●

*risk of an adverse effect (see ’cause of variable or unfavourable effect’)

Cause of variable or unfavourable effect

Nitrate

The effect of nitrate supplementation depends on dose, and adaptation of the animal (i.e. a stepwise increase of dietary inclusion up to the target level), and animal type. It is recommendable to evaluate for the highly varying systems of sheep production what dose to apply to prevent for example impact on feed intake. As nitrogen is added to the ration, ammonia and nitrous oxide emissions may increase if the ration is not optimized accordingly, for which options may be very limited in case of full grazing or pastoral systems.

*Literature references*	Nitrate
Li et al. (2012)	An initial investigation on rumen fermentation pattern and methane emission of sheep offered diets containing urea or nitrate as the nitrogen source
El-Zaiat et al. (2014)	Encapsulated nitrate and cashew nut shell liquid on blood and rumen constituents, methane emissions, and growth performance of lambs
Almeida et al., 2021	Meta-analysis quantifying the potential of dietary additives and rumen modifiers for methane mitigation in ruminant production systems
Torres et al, 2023	Potential of nutritional strategies to reduce enteric methane emission in feedlot sheep: A meta-analysis and multivariate analysis
Raphélis-Soissan et al., 2014	Use of nitrate and Propionibacterium acidipropionici to reduce methane emissions and increase wool growth of Merino sheep
Rivelli et al. 2025	Efficacy of 3-NOP applied in drinking water on enteric methane reduction in sheep