The following answer was provided by Charles Schwab, professor emeritus of animal sciences at the University of New Hampshire and dairy nutrition consultant, and included in the proceedings of the Southwest Nutrition Conference, which was held Feb. 25-26 in Tempe, Ariz.
Q: How do you optimize amino acid formulations for lactating dairy cows?
A: We consider five steps as being important to maximizing milk components and metabolizable protein (MP) utilization through amino acid formulation.
1. Feed a blend of high-quality forages, processed grains, and byproduct feeds to provide a blend of fermentable carbohydrates and physically effective fiber that maximizes feed intake, milk production, and yield of microbial protein. Microbial protein, based on research to date, has an excellent AA composition for lactating dairy cows. The average reported concentrations of lysine and methionine in bacterial true protein approximate 7.9 percent and 2.6 percent, respectively; values that exceed the concentrations in nearly all feed proteins (NRC, 2001), and values that exceed the optimal concentrations in MP as estimated by the NRC (2001), CPM-Dairy (v.3.0.10) and AMTS. Cattle (v.2.1.1) models (see Table 1). Realizing maximal benefits of feeding a balanced supply of fermentable carbohydrates on feed intake, milk production, and yields of microbial protein requires use of high-quality feeds, adequate intakes of physically effective fiber, well-balanced and consistent diets, unlimited supplies of fresh water and superior bunk management.
2. Feed adequate but not excessive, levels of rumen-degradable protein to meet rumen bacterial requirements for amino acids and ammonia. Realizing the benefits of feeding a balanced supply of fermentable carbohydrates on maximizing yields of microbial protein also requires balancing diets for RDP. Rumen degraded feed protein is the second largest requirement for rumen microorganisms. It supplies the microorganisms with peptides, AA and ammonia that are needed for microbial protein synthesis. The amount of RDP required in the diet is determined by the amount of fermentable carbohydrates in the diet. Diet evaluation models differ in their estimates of RDP in feeds and animal requirements. The NRC (2001) model typically predicts RDP requirements of 10 to 11 percent of diet DM. Regardless of the model, use the predicted requirements as a guide and fine-tune according to animal responses. Monitor feed intake, fecal consistency, milk/feed ratios, milk fat concentrations, and MUN to make the final decision. A common target value for MUN is 10-12 mg/dl, but values lower than this are not uncommon in high-producing cows. Don't short-change the cows on RDP ... carbohydrate balancing can be negated with an inadequate supply of RDP. A deficiency of RDP will suppress the ability of the microorganisms to reproduce, but they can continue to ferment carbohydrates. This will often result in lower than expected milk/feed ratios because of lower than expected synthesis of microbial protein. Avoid over-feeding feeding RDP to the point that rumen ammonia concentrations markedly exceed bacterial requirements. Not only does it result in wastage of RDP, but research (e.g., Boucher et al., 2007), as well as a summary of N passage studies where rumen ammonia concentrations were also measured (Peter Robinson, personal communication), indicate that rumen ammonia concentrations in excess of bacterial requirements decreases flows of microbial protein to the small intestine.