Feed Methanogenic Inhibitors
System: Sheep
Applicability
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.
Effects on GHG emissions
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)
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 |
Legend
| ● – Small effect (<5%) | o – No effect | ? – Effect unknown |
| ●● – Medium effect (5-20%) | ● – Unfavourable effect | |
| ●●● – Large effect (>20%) | ● – ● – Variable effect (depending on farm characteristics or way/level of implementation) | |
Effect per emission source
| Mean effect on absolute emission from | Animal | Manure storage | Feed and forage production | Barn | |||
| CH4 | CH4 | N2O | CO2 | N2O | LUC | CO2 | |
| Nitrate | ●● | ● | ● | ● | |||
*risk of an adverse effect (see ’cause of variable or unfavourable effect’)
Legend
| ● – Small effect (<5%) | o – No effect | ? – Effect unknown |
| ●● – Medium effect (5-20%) | ● – Unfavourable effect | |
| ●●● – Large effect (>20%) | ● – ● – Variable effect (depending on farm characteristics or way/level of implementation) | |
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.
Other Effects
Effects on yield and cost-effectiveness
| Yield | Labor | Costs and revenues | ||||
|---|---|---|---|---|---|---|
| Animals | Crops | Time | Capital investment | Operational Costs | Revenues | |
| Nitrate | ●-o | o | ● | ●●● | ●–● | |
Legend (thresholds differ per indictor and can be found in the tooltip)
| ● – Small favorable effect | o – No effect | ? – Effect unknown |
| ●● – Medium favorable effect | ● – Unfavourable effect | |
| ●●● – Large favorable effect | ● – ● -Variable effect (depending on farm characteristics or way/level of implementation) | |
Effects on other sustainability aspects
| Risks of trade-offs | Potential synergies | |
|---|---|---|
| Nitrate | Ammonia emission, Animal welfare, Societal and cultural acceptance, Farm labour safety |
| 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 |