ABSTRACT
Amino acids available for small intestinal absorption in ruminants are derived from microbial proteins synthesized in the rumen, undegraded dietary proteins which escape the rumen and endogenous secretions. The most extensively investigated amino acid analog has been methionine hydroxy analog (MHA). If MHA exerts its influence on milk fat through alterations in rumen metabolism, it seems unlikely that stage of lactation would play a significant role in responsiveness to MHA. Many other derivatives and analogs of methionine have been investigated for their potential ability to escape microbial destruction and improved methionine status. Polymeric encapsulation offers the greatest opportunity to increase postruminal amino acid supply and composition in practical production diets. While lipid encapsulated products contain only about 20% amino acids, the polymer protected products generally contain 70 to 80% amino acid. This amino acid density offers the obvious advantage of being able to provide the amino acids with relatively low levels of the polymer complex in the diet.
