The objective of this review was to discuss microbial protein synthesis and the effects of sources and concentrations of nitrogen and carbohydrate on microbial protein synthesis. Even though ammonia-N is a satisfactory source of nitrogen for the growth of the majority of rumen microbes, substitution of intact protein for urea usually stimulates ruminal microbial protein synthesis. While protein sources high in degradable intake protein (DIP), such as soybean meal, appear to have properties that optimize microbial protein synthesis, protein sources low in DIP, such as fish meal, appear to limit microbial protein synthesis apparantly because of the low ruminal digestibility of fish meal. Similarly, a mixture of structural and non-structural carbohydrate sources is necessary for maximal microbial protein synthesis in the rumen.

The objective of this review was to discuss microbial protein synthesis and the effects of sources and concentrations of nitrogen and carbohydrate on microbial protein synthesis. Even though ammonia-N is a satisfactory source of nitrogen for the growth of the majority of rumen microbes, substitution of intact protein for urea usually stimulates ruminal microbial protein synthesis. While protein sources high in degradable intake protein (DIP), such as soybean meal, appear to have properties that optimize microbial protein synthesis, protein sources low in DIP, such as fish meal, appear to limit microbial protein synthesis apparantly because of the low ruminal digestibility of fish meal. Similarly, a mixture of structural and non-structural carbohydrate sources is necessary for maximal microbial protein synthesis in the rumen.