Development of Urea Products as Rumen Slow-Release Feed for Ruminant Production: A Review

Dietary protein plays an important role in the nutrition of ruminants, besides providing amino acids; it is also a source of nitrogen for the synthesis of microbial protein. Ruminants have the ability to utilize non-protein nitrogen compounds as N sources for rumen microbial protein synthesis. The use of urea as a protein replacement is attractive in ruminant diets because of its low cost compared with other NPN soures and protein feeds such as soybean meal with high rumen degradability. However, the amount of urea can be used in diets is rather limited due to its rapid hydrolysis to ammonia-nitrogen in the rumen by microbial enzymes, resulting in accumulation and escape of ammonia-nitrogen from the rumen. Slowly ruminal released urea compounds, as a replacement for urea in ruminant rations, have a long history in ruminant feeding. This interest in slowly rumen released nitrogen compounds primarily stems from their potential to slow ammonia release post-feeding, thereby decreasing peak ammonia concentrations in the rumen that lead to its inefficient utilization by ruminal microorganisms, and increased absorption from the rumen. This would also decrease the metabolic cost associated with converting ammonia to urea in the liver, while providing a steady supply of ammonia to rumen bacteria between meals. This review describes the utilization of urea and development of slow-release urea products in ruminants. Recent studies of supplementation of slow-release urea products on rumen fermentation, microbial protein synthesis, and milk production in ruminants are also summarized.