Traditionally, methionine and lysine have been considered the first two amino acids limiting milk production and milk protein synthesis in typical North American dairy diets.
However, Penn State research has determined that histidine also can be a limiting amino acid in high-producing dairy cows fed corn silage and alfalfa haylage-based diets deficient in metabolizable protein. This is primarily a result of the relatively low histidine concentration in microbial protein synthesized in the rumen.
These findings suggest that when nutritionists formulate diets for high-producing dairy cows fed metabolizable protein at or below dairy NRC (2001) requirements, they should also balance for digestible histidine supply.
The latest issue of the Penn State Dairy Digest looks at this topic in more detail.
Source: December 2012 Penn State Dairy Digest