Abstract
Modern dairy cows are dependent on viable protein sources to maintain adequately high and persistent milk production. However, qualified protein sources, such as soybean meal are usually high and not easily available. Feed-grade urea (FGU) has been utilized in dairy diets for decades to help economically. Some portions of dietary nitrogen are a point in this case. Nonetheless, FGU can be considered a potential source of microbial protein, only if adequate timely fermentable nitrogen sources are supplied to the rumen microbes for successful microbial protein synthesis. In addition, FGU has a rapid degradation rate in the rumen, which may cause microbial toxicity and excessive ammonia and urea production, leading to environmental issues. It means that the effective use of FGU would be challenging. Accordingly, by improving rumen synchrony and metabolism and cow performance such limitations can be overcome through the development of slow-release urea (SRU). However, compared with FGU recent studies do not fully support the practical and economic effectiveness of SRU, towards improved cow metabolism and performance. More experiments particularly with varying dietary fermentable energy sources are required to conclusively decide if SRU may be a practical contemplation towards increased dairy production sustainability or it is just an expensive useless fantasy.