Prediction of Ammonia Emission from Dairy Barns using Feed Characteristics. Part II: Relation between Urinary Urea Concentration and Ammonia Emission.

Emission of NH3 from dairy barns can be reduced substantially by changing the cows’ diet. Emission of NH3 is reduced most effectively when dietary changes result in a reduction of urinary urea concentration. The objective of this research was to predict NH3 emission from dairy barns for various diets, using feed characteristics, and climate, barn, and slurry related parameters. Model results were validated using experimental data. Cows were fed one of nine diets, which was a combination of three rumen degradable protein balances and one of three roughage compositions. Each diet was repeated once. Measured parameters included herd, diet, urine, slurry, barn and climate characteristics, and emission of NH3 from the barn. For a wide range of diets and barn conditions, observed NH3 emission from a dairy barn can be predicted accurately using a combination of existing nutrition-emission models. Accuracy of prediction improved considerably, however, when observed emissions during four diet treatments were omitted due to suspected technical failure of the emission measurement equipment. Results also show that NH3 emissions in common practical situations will range from about 3.3 to 16.3 kg per cow per 190 d. To reduce NH3 emission in practice, farmers should maximize the diet’s grass content, and at the same time, minimize its rumen degradable protein balance level. Currently, however, farmers need additional information to compose such a low-emission diet, which should fulfill also the intestine digestible protein and net energy-lactation requirements of a cow.