“…Often the limiting factor in MPS is the availability of energy from fermentation with its rate of production similar to the rate at which the microbes can utilize it. Lewis and McDonald (1958) and Phillipson et al (1962) revealed that the non-structural carbohydrates (sugars and starches) were efficient in decreasing ruminal ammonia concentrations by increased MPS; subsequently, Stern et al (1978), identified that having greater ratios of structural carbohydrates (pectins, cellulose, and hemicellulose) compared to non-structural carbohydrates actually increased ammonia concentrations thereby decreasing MPS. Russell et al (1992) separated the rumen microbes into 2 groups, those that ferment structural carbohydrates, grow slowly, and use ammonia as a primary N source, and those that ferment non-structural carbohydrates, grow rapidly, and utilize ammonia, AA, and peptides as a N source.…”