There is a wide variation in nitrogen-use efficiency across NI dairy farms, a study by the Agri Food and Biosciences has found.
Nitrogen-use efficiency is a measure of the amount of nitrogen consumed by a dairy cow which subsequently ends up in milk protein.
The study was conducted on 26 local dairy farms and found that average nitrogen-use efficiency ranged from 25% to 34%.
Crude protein content of dairy cow diets was one of the main factors influencing the nitrogen utilisation.
For example, at a total diet crude protein of 15.5%, approximately 31% of nitrogen consumed was converted to milk protein, so almost 70% was excreted in manure.
It compares to a total diet crude protein level of 18.5%, where only 26% of nitrogen was utilised.