Consequences of nitrogen losses in ruminants

It is well known, that ruminants show a low efficiency when it comes to nitrogen utilization. Besides other factors, diet plays an important role when it comes to minimize those losses. Get in the first part of this article general insights about nitrogen losses in dairy cattle and an overview about the consequences of ammonia excretion for the environment.

Nitrogen losses in dairy cattle

In ruminants, nitrogen utilization is relatively inefficient, with 50 to 80% of the nitrogen consumed being excreted as urea-N (mainly in urine) and other organic nitrogen components (mainly in feces). Nitrogen losses are partly from urine losses (from ammonia losses in the rumen and metabolic losses in the liver) and partly from undigestible protein losses (in the feces).

In Figure 1, nitrogen excretion increased particularly with nitrogen intake. While the rate of feces nitrogen losses decreased with the nitrogen intake:
- 0.40 g nitrogen losses per g nitrogen intake for 200 g nitrogen intake
- 0.25 g nitrogen losses per g nitrogen intake when dairy cows eat 750 g/day of nitrogen.

In contrast, the conversion of dietary nitrogen to urinary nitrogen increased exponentially with increasing nitrogen intake.

Figure 2. Urinary nitrogen losses in function of rumen balance between fermentable energy and degradable protein (Sauvant et al, 2015)

Parallelly, this nitrogen excretion decreases with:  
- the respect of the balance between protein requirements and protein in the diet.
- the balance between fermentable energy and degradable protein in the rumen (Figure 2).

Ammonia (N-NH3) is volatilized after nitrogen excretion in manure whether under confinement or grazing conditions (Figure 3). Ammonia production averages 60 g/head/day in dairy cows. N-NH3 is increased by the crude protein level of the diet, feed intake but decreases with milk production.

Figure 3: ammonia emissions from dairy cattle housing (Bougouin et al, 2016)

In addition, outdoor temperature and wind increase ammonia volatilization due to activation of urease activity in manure. The manure handling system and housing type also have an impact on ammonia production (Figure 3).

In conclusion, to reduce ammonia production, we need to optimize the protein efficiency in the diet, housing system, manure management, and manure application in the land.

Consequences of ammonia excretion for the environment

Figure 1: Ammonia formation and volatilization from manure.

The nitrogen excreted in ruminants' urine is transformed by an enzyme activated in manure (urease) capable of converting the liquid ammonia into gas ammonia (NH3) (Figure 1).
Agriculture and livestock account for 90-95% and 50 % of ammonia emissions, respectively (in the USA).

Figure 2: Consequences of nitrogen losses for the environment (water pollution, air pollution and Carbon foot print).

This liquid ammonia, spread on the soil, will be transformed into nitrogen oxides (N2O) and nitrates (NO3) (Figure 2).

Together, this manure production and fertilizer contributes directly to water pollution. Ammonia (NH3) is transformed into ammonium depending on climatic conditions (temperature, wind).

A nitrate level (NO3-) higher than 50mg/L (water standards) in rivers is often sufficient to promote eutrophication. This unbalance of nutrients in the water (excess of nitrates and phosphorus) will help the growth of algae and aquatic plants. But when these plants die, they consume a large quantity of oxygen with harmful consequences on the ecosystem balance. This pollution will reduce life in freshwater: less plankton, fewer fish, less biodiversity. If there is a lack of bicarbonates in the water, ammonium will provoke water acidification resulting in a reduction in the fish and amphibian population.


A problem with nitrogen pollution is that a high concentration of farm animals generates many manure, mainly in slurry. In volume, this cannot be easy to store and use as fertilizer.

An increase of greenhouse gasses (carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) in the atmosphere leads to global warming. Increasing concentrations of nitrous oxide (N2O) and methane (CH4) are particularly dangerous as both have a much higher oxidation number and therefore contribute more to the greenhouse effect than carbon dioxide:

  • Methane (CH4) with a global warming potential 28 times greater than CO2.
  • N2O with a global warming 310 times greater than CO2.

Agriculture is responsible for 24 % of the carbon footprint.  In 2011, the Food and Agriculture Organization (FAO) showed that agriculture produces the equivalent of 5.3 billion of Eq CO2 T/year. 39% comes from enteric fermentation (methane produced by rumen fermentation), and 25 % comes from nitrogen (NO2). Agricultural N2O emissions are mainly soil emissions due to microbial processes of nitrification and denitrification. Nitrogen added to the soil can contribute directly or indirectly to N2O emissions. According to some estimates, manures constitute 17% of the sources of N2O in the USA. Thus, N and NH3 volatilization from manure can directly contribute to Greenhouse Gas (GHG) emissions from animal agriculture.

Due to its high reactivity, NH3 reacts with atmospheric acids such as sulfuric and nitric acids to form ammonium sulfate, ammonium bisulfate, or ammonium nitrate, which are considered fine particulates (<2.5 µm). These particulates contribute to air pollution, which, on a global scale, is estimated to cause up to 2 million premature deaths annually (WHO 2005). These fine particulates (PM2.5) are considered among the most dangerous for lung diseases.

Similarly, nitrous oxide (N2O) in the air is also responsible for air pollution and rain acidification, and tree death in the forests.

In conclusion, ammonia emitted by livestock has an impact on the environment and human health. It contributes to eutrophication of surface waters, nitrate contamination of groundwaters, soil acidity, fine particulate matter formation, and global warming.

Thierry Aubert

Thierry Aubert

Thierry Aubert can look back on 15 years of experience in the premix, feed and meat industry. Since the beginning of his career, Thierry is in regular exchange with the farmers to understand their challenges and needs. In 2013 he joined Delacon as Species Leader Ruminants. With his team, he is in charge of the global product development for the ruminant species and customer technical support. Since spring 2018, his task areas have been extended: At the moment, he is also responsible for the coordination of the Reginal Technical Managers worldwide. In his leisure time, he likes to go running and already participated in several marathons.

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