Reducing the Crude Protein in Dairy Rations to help Reduce Ammonia Emissions

24 March 2020

by Claire Beckett, Dairy Technical Support Coordinator 

Agriculture contributes to Northern Ireland’s ammonia emissions, with cattle accounting for a significant proportion of these emissions.

The agricultural industry is under pressure to reduce ammonia emissions due to the adverse effects on human health, wildlife and the environment.

Ammonia emissions also represent an economic loss to farmers due to inefficient use of protein. Excess dietary protein is excreted in urine as urea. When urine and faeces are in contact, urea is broken down by an enzyme called urease and ammonia is produced. Although there is a direct link between excess protein and ammonia emissions, it’s not just as simple as reducing crude protein of diets without a trade-off in productivity and health.

Although the biggest gains in reducing ammonia emissions is through slurry management, the government are also looking to the animal feed industry for potential ways to reduce ammonia emissions through nutrition, by reducing the crude protein of diets. Significant progress has already been made in the pig and poultry industry and now the dairy industry is coming under the same pressure to reduce crude protein of diets.

In many cases it is possible to reduce the crude protein of the diet by more accurately meeting and balancing the nutritional needs of the cow. Various ways include:

  1. Accurately balancing ‘rumen available’ and ‘rumen bypass’ protein to maximize protein digestion. To best meet the nutritional requirements of the cow, maximize the rumen available proportion without feeding excess, then use bypass protein to meet the remainder of the requirements. Good quality grass silage and grazed grass is often high in rumen available protein and therefore may only need supplemented with a small amount of rumen bypass protein, such as protected soya bean meal or rapeseed meal (Sopralin/Rapralin) or prairie meal.
  2. Ensure the dietary energy and protein degradation rates are aligned. Maximise the amount of rumen degradable energy (starch, sugar & fibre) to capture the rumen degradable protein. Milk urea is a good indicator of rumen energy and protein balance and a milk urea between 19-23mg/dl is reflective of a well-balanced rumen.
  3. Cows have a requirement for amino acids (the building blocks of protein), rather than protein per say, but diets often over supply protein just to meet certain amino acids requirements. Methionine is usually the most deficient amino acid in dairy rations, followed by lysine. Formulating compound feeds using specific raw materials can help meet amino acid requirements e.g. rapeseed meal is rich in methionine and soya bean meal is rich in lysine. Any shortfalls can be met by supplementing bypass amino acids.
  4. Feeding a highly glucogenic diet (a diet capable of producing a lot of glucose) is essential to meet the cow’s energy requirements. If glucogenic nutrients are deficient (as is the case in many early-lactation diets), amino acids will be used by the cow for the production of glucose. This is an inefficient use of protein.Feeding higher levels of starch (cereals), particularly bypass starch (maize meal and maize silage), will support higher levels of glucose production.
  5. Feeding sufficient levels of protein during the dry period (particularly the close-up period) allows for protein levels to be built-up within muscle tissue as a reserve for early lactation.
  6. Grazing cows – although protein is typically over supplied in a grazing scenario due to elevated protein levels in grass, urine and feaces rarely come into contact therefore much less ammonia is emitted compared to in confined systems.


The NutriOpt dairy model is a ration formulation system developed by Trouw Nutrition, which takes account of where and at what rate different feed ingredients are digested along the total digestive tract. The system allows rations to be more precisely balanced for energy and protein, amino acids and glucogenic nutrients, enabling the crude protein content of rations to be lowered, whilst still meeting the nutritional requirements of the cow by improving nitrogen efficiency and utilization. This helps capture more value out of the protein in the diet. An accurate forage analysis, which measures specific NutriOpt parameters, is key to fully exploiting the potential of the Model in optimizing rations.