Slow-release non-protein nitrogen sources in animal nutrition: A review

Today, feeding protein supply according to need in high-yielding lactating cows has become a big challenge. Protein is the most costly bulk constituent of animal diet, and the price of protein sources is increasing steadily, which is different from milk price rising. Therefore, one way for farmers to reduce feed costs is to reduce dietary protein share. Ruminants obtain their amino acids from 2 sources: amino acids from ruminally undegraded protein (RUP) and microbial protein synthesized in the rumen. A key goal in ruminant nutrition strategies, maximizing the use of rumen degradable protein (RDP), is through its efficient conversion into microbial protein. Urea is a supplement and a possible source of non-protein nitrogen (NPN) in ruminants' diets which meets bacteria's ammonia needs. Rumen ammonia sources include protein, peptides, amino acids, and other nitrogen-bearing compounds. As urea, uric acid, nitrate, and possibly nucleic acid are rapidly converted to ammonia, the ammonia reservoir indicates that the ruminal metabolism of ammonia is relatively small. Bacteria in the rumen can obtain between 40 and 95 percent of their nitrogen demand from ammonia, depending on their diet. Using NPN (non-protein nitrogen) as a reliable nitrogen source for ruminants was recognized over 100 years ago. Urea is quickly released in the rumen, its use in the diet is limited due to ammonia toxicity. So, the solution to this problem is that the product in nitrogen release rate from urea changes according to the digestion of fibers in the rumen. In the past, several slow-release products were made and evaluated. Slow-release urea (SRU) sources will also affect microbial growth and livestock performance compared to conventional plant protein sources. Acceptance of SRU sources, depending on their price compared to conventional plant protein ingredients is feasible. Studies has shown that the use of slow-release urea did not have a negative effect on digestibility, rumen parameters, milk production and livestock performance. Single-cell protein (SCP) is an emerging alternative protein source, currently being mainly studied for chicken and aquatic species.Finally, it is concluded that slow release urea can be used in feeding ruminants without any side effects.