The diet of dairy cows contains nitrogen, mainly in the form of protein. However, the efficiency of nitrogen use by dairy cows is low, with only about 30% of the nitrogen consumed being converted to milk protein. Much of the remaining nitrogen is excreted in manure, which has a number of implications:

Nitrogen is lost from manure (during housing, during manure storage and during spreading) as ammonia gas, and when it settles on sensitive habitats it can lead to biodiversity loss and soil acidification.

· Ammonia from manure can react with pollutants in the atmosphere to form fine particles, which can cause respiratory problems in humans.

· Nitrogen in manure can also be lost as nitrous oxide, a potent greenhouse gas with a global warming potential almost 300 times that of carbon dioxide.

· Losses of nitrogen from manure to rivers, mainly through leaching, can lead to nutrient enrichment in fresh and coastal waters (the EU Nitrates Directive was established to address this issue).

· Protein is generally the most expensive component of the diet of dairy cows, so the inefficient use of dietary nitrogen represents an economic loss. In addition, the cultivation of protein foods such as soybeans threatens sensitive ecosystems in some parts of the world.

Recognizing these challenges, DAERA, supported by co-funding from John Thompsons and Son Ltd and Trouw Nutrition Ltd, commissioned AFBI to conduct an extensive research program designed to identify strategies to improve the efficiency of nitrogen in dairy cows. Work to be undertaken under this research partnership will include reviewing the existing scientific literature to identify the following: relationships between dietary protein and ammonia excretion from manure, recent research on protein feed, protein feed systems adopted in Europe and approaches to assess the protein status of cows based on the analysis of milk, blood and manure. In addition, the research will include an extensive data modeling exercise to examine factors in the efficiency of nitrogen use in dairy cows, with this work involving data collected from approximately 40 studies conducted at the AFBI over the past 25 years. The project will also include a series of comprehensive lactation studies in which the direct effect of protein nutrition on cow performance will be monitored. These studies will also examine the effects of diet on milk and blood urea levels, ration digestibility and the rumen microbiome (the latter in partnership with QUB), and seek to identify alternative approaches, such as the use of medium infrared (MIR) analysis of milk to predict the efficiency of nitrogen use. The economics of adopting low protein diets will also be examined.

There is currently considerable pressure, which will continue to increase, for the dairy sector to improve the efficiency with which dairy cows use feed nitrogen. This major project, through the adoption of a holistic research approach, has the potential to help improve the efficiency of nitrogen use in the local dairy sector and ultimately reduce nitrogen losses to the environment.