During enteric fermentation in the rumen, the main route for the disposal of hydrogen (H2) is via methanogenesis. During this process, carbon dioxide (CO2) is reacting with hydrogen (H2) to form CH4. This mechanism is essential for the continuation of the rumen fermentation. However, this methanogenesis is resulting in the formation of CH4, which is a loss of dietary energy, but also contributing to global warming. 

CO2 + 4H+        à          CH4 + 2H2O

When nitrate (NO3-) is added to the diet, this will act as an alternative H2 sink and will form nitrite (NO2-). NO2- will on its turn react with H2 and ammonia (NH4+) will be formed. NH4+ is the end product en can by used by rumen microbes to form protein. 

NO3- + H2     à     NO2- + H2O
NO2- + 3H2 + 2H+     à    NH4+ + 2H2O

When nitrite is not quickly reduced to ammonia, it can be absorbed across the rumen wall and reduce the oxygen-carrying capacity of the blood to the tissues resulting in a reduced performance. In addition, high levels of NO2- in the rumen will have a negative impact on feed intake. Nitrite poisoning can, in sever case, cause death of the animal. 

A research group in the United States (Feng et al. 2020) developed an equation to calculate the reduction potential of nitrate. It is indicated that the nitrate effect on enteric CH4 production is significantly affected by cattle type, nitrate dose (g/kg DM) and DMI (kg/day). The mitigating effect is greater in dairy cattle compared to beef cattle. The equation is as follows: 

Beef enteric methane reduction rate (%)
-10,1 - (0,911 x nitrate dose) + (0,691 x DMI)

Nitrate is commercially available. Cargill has a patented product containing nitrate, as well as sulphate, which is also effective in reducing methanogenesis. The additive is in the form of a powder or a compacted/granulated solid. It can be added in the premix/ration or can be used in lick blocks. This additive is advised to feed at in inclusion rate, ranging from 16-2500 g/animal/day. The nitrate is preferable an inorganic nitrate salt, such as Calcinit (commercially available from Yara). The sulphate compound is preferably a soluble inorganic sulphate salt. When nitrate on itself is added to the diet, it is advised to add a maximum of 1% of the total ration. 

Side note: In grazing cattle, when the grass already contains high levels of nitrate, feeding this additive on top will not have an additional effect. 

Impact on:

- Socio- economic resilience: When adding an additive to the diet, this will increase the cost for the farmer. However, the product of Cargill will partially replace the protein content in the diet, which will not increase the costs.
- Animal health and welfare: When ruminants consume a high nitrate feed, some of the nitrate cannot be converted immediately to nitrite and finally, to ammonia. This situation causes both nitrate and nitrite to accumulate in the rumen. Nitrate is continually being released from the feed being digested in the rumen, so the addition of new nitrate into the rumen intensifies the problem, leading to nitrate poisoning. Nitrite will be absorbed through the rumen wall and enter the blood stream. This will reduce the oxygen-carrying capacity of the blood and impair animal performance. In extreme cases, nitrate poisoning can lead to the death of the animal. 
- Production efficiency and meat quality: No changes in productivity. An improved feed consumption and animal productivity can be realized.
- Environmental sustainability: Reduction of CH4, can be calculated with an equation.


Link to patent of Cargill