Use of urea as nitrogen source (nitrogen emissions)

Last update: 2 June 2023

• Action: Reduction of nitrates and ammonia emmission in the environment.
• Animal category: Ruminants with fully functional rumen.
• Technique: Decreasing dietary crude protein levels in compound feed by adding up to 1% urea per kg of total Dry Matter Intake, as substitute of nitrogen from vegetable protein.
• Mode of action: Urea is hydrolysed in the rumen to ammonia and CO2 by the bacterial enzyme urease; ammonia from urea is used by the ruminal microbiota for synthesis of microbial proteins which are subsequently digested in the intestine.
• Potential efficacy: The slow release form may increase feed efficiency up to3% and nitrogen use efficiency up to +4% for dairy cows; may lower emissions of ammonia and N₂O from the faeces and urine between 2.7% and 3.1% (i.e. -12 to -13 g/cow/d) and N excretion intensity by 3.6% to 4.0% ( i.e. -0.50 to -0.53 g N/kg milk).
• Nature of evidence of efficacy: Peer-reviewed scientific publications (meta-analysis); EFSA assessment.
• Factors impacting on efficacy: Variation in rumen function, including duration and extent of rumen digestion.
• Mode of use: Incorporated into compound feed (complete or complementary).
• Requirements/limitations: Urea should be coated to prevent rapid hydrolysis of urea to NH₃ that is toxic; the utilization of urea in ruminant nutrition is limited due to its rapid hydrolysis to NH₃ in the rumen, exceeding the rate of carbohydrate fermentation in the rumen; doses up to 1 % of complete feed DM (corresponding to 0.3 g/kg bw/day) is considered safe; the substance must be added in a mixture by a registered feed business operator applying HACCP (R183/2005); not permitted in organic farming.
• Economic consequences: Reformulation of protein sources may reduce feed cost.
• Other considerations: The asynchrony between rumen NH₃ production and available fermentable energy could exert a negative effect on the efficiency of microbial protein synthesis; reformulation of diets with slow release urea can result in significant changes in the composition of raw materials in dairy diets.
• References:
  • Salami SA et al. (2021). Meta-analysis and sustainability of feeding slow-release urea in dairy production. PloS ONE 16(2): e0246922. https://doi.org/10.1371/journal.pone.0246922
  • EFSA (2012). Scientific Opinion on the safety and efficacy of Urea for ruminants. EFSA JournalVolume 10, Issue 3 2624. https://doi.org/10.2903/j.efsa.2012.2624
• Other techniques: Adding rumen protected amino acids to feed.