Dairy Cow Feed Rations and Ammonia Emissions
On farms, reducing nitrogen losses in livestock not only helps to preserve the environment, but also improves the farm's bottom line.
Ruminant livestock are not very efficient at using the nitrogen they take up in feed. If rations are very precisely calculated, 30 to 35 percent of the nitrogen in feed proteins and non-protein compounds becomes a component of milk. The rest of the nitrogen is excreted from the body mainly in urine and faeces. About 60 to 80 per cent of urinary nitrogen is in the form of urea.
Urea concentration in urine is an important indicator of ammonia emissions in dairy farming. It is possible to adjust both the urine output, the urinary urea concentration and the total manure output with the feed ration. It must be clearly understood that urine and faeces separately emit very minimal quantities of ammonia, but only after they reach the floor surfaces in the housing and these two fractions of excreta physically mix, ammonia is released.
There are additional factors that influence the evaporation of ammonia in cow housing. These include temperature, air velocity, pH, size of floor surfaces, moisture content of manure and storage time. For example, high pH and temperature contribute to increased ammonia emissions. Dairy cow manure typically has a pH between 7.0 and 8.5, which allows ammonia to be released into the atmosphere quite quickly.
The deposition of atmospheric ammonia and chemical compounds resulting from atmospheric chemical reactions with ammonia (i.e.ammonium aerosol) is thought to contribute to water and soil acidification and eutrophication.
Thus, one solution is to balance feed rations as closely as possible to the amino acid needs of the cow: the amount of crude protein in the diets of high-yielding cows can be safely reduced, allowing farms to maintain high milk yields (above 35 kg per cow per day) while improving nitrogen use efficiency
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