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Pig Defecation Better at Forming Ammonia

Researchers from the Department of Chemical Engineering, Biotechnology and Environmental Technology at the University of Southern Denmark, are the first to measure and compare the activity of the ammonia-forming enzyme in faeces and manure from pigs and cows. Their conclusion is clear; pig faeces forms ammonia faster. The researchers will now try to find a cheap and effective method to stop the formation of ammonia.

During the periods when slurry is spread on the fields, large parts of Denmark smell. This is partly due to the smelly ammonia in the manure. Associate Professor at the Department of Chemical Engineering, Biotechnology and Environmental Technology at SDU Henrik Karring, has together with PhD student Xiaorong Dai studied the process responsible for the formation of ammonia in manure. The new study clearly shows that there is a major difference in how quickly ammonia is formed in manure from pigs and cows.
Research results were recently published in the scientific journal PLOS ONE.

Ammonia from slurry is a major environmental problem

Ammonia is a compound of nitrogen and nitrogen is used as a nutrient in agriculture, however, too much nutrition can put nature out of balance. It is called nitrogen pollution and the production of pigs and cows contribute significantly to this. Nitrogen pollution with ammonia, among other things, therefore constitutes a big environmental problem both in Denmark and on an international scale. Moreover, the ammonia evaporation from the slurry, impair the indoor climate in the stables massively.

“When urine and faeces are mixed and become liquid manure, the bacteria in the faeces transform the urea in the urine to vaporisable ammonia. Some of the defecation bacteria contain the enzyme urease which is responsible for the enzymatic transformation of urea to ammonia,” explains Henrik Karring.
Without the urease enzyme, the bacteria cannot take advantage of the amount of nitrogen contained in the urea, to grow.

Blocking the formation of ammonia in liquid manure

 Until now, it has been assumed that the urease activity in slurry was similar for pigs and cows, but the new study clearly demonstrates that pig faeces is fastest when it comes to converting urea to ammonia. A major reason for this difference is that the urease enzyme activity is more than twice as high in pure faeces from pigs compared to cows.

When the researchers measured the formation of ammonia immediately after the mixing of urine and defecation from pigs and cows, they found that in one minute, approximately 1.5 millimoles ammonia was formed in a litre of liquid manure from pigs, while the corresponding figure for fresh manure from cows was approximately 0.3 millimoles.

The new measurements thus increase the understanding of specific parameters for the activity of urease in faeces from pigs and cows. This means that there can be made more accurate models for the formation of ammonia in the liquid manure and thus also for the quantity of ammonia that evaporates from the slurry.

“Our studies have given us a good starting point to continue research to find a biotechnical solution to ammonia formation in the slurry. I hope that we in the near future find an effective and cheap method to block the formation of ammonia in manure,” says Henrik Karring.


An enzyme is a protein which catalyses a specific chemical reaction so that it proceeds more quickly. An enzyme-catalysed reaction is therefore often faster than the non-catalysed reaction. Since the enzyme is not used in the reaction, a single enzyme molecule can be reused several times. The enzyme urease is known within medical science because of its involvement in the formation of i.a. kidney stones and gastric ulcers. The bacterium Heliobacter pylori which is thought to be the cause of various cases of gastric ulcers, produces large amounts of urease which helps to ensure that the bacteria can cope with the low pH value found in the stomach. Urease was the first enzyme to be crystallised (1926) and the first enzyme that was found to contain nickel (1975). Today, the sciences only know of a few enzymes that contain nickel. Urease is one of the most efficient enzymes know to science.

For more information, please contact

Associate Professor Henrik Karring at or phone: 2135 6350