Formulating for Better AA Efficiency

NASEM Updated Using AA Efficiency

The objective: To balance dairy rations for essential amino acids (EAA) rather than their aggregate, metabolizable protein (MP). This factorial approach helps optimize milk protein yield, improve cost efficiency, and reduce nitrogen excretion.

Last September, the NASEM committee that focused on dairy cattle requirements updated the software linked to the guide released in 2021. Dr. Hélène Lapierre, a lead researcher with Agriculture and Agri-Food Canada's Sherbrooke Research and Development Centre, was one of the co-authors, mainly involved in the protein and AA chapter.

Efficiency of utilization

Advanced dairy feed programs, Lapierre notes, now use the efficiency of utilization (Eff) of MP to estimate MP requirements. NASEM applied this approach to EAA, which recognizes requirements of individual EAA.

NASEM considered the Eff of each EAA to vary similarly for scurf, metabolic fecal protein (MFP), milk true protein yield (MPY), and growth. Therefore, for each ration and associated MPY, the Eff is calculated as the quotient of each EAA in [(scurf+MFP+MPY+growth)/adjusted supply×100]. The "adjusted supply" excludes endogenous urinary loss, and, if the cow is pregnant, adjusts for associated EAA accretion. 

Multiple advantages

"The concept of the Eff of EAA fulfills multiple purposes," Lapierre says. "First, we can use it to determine recommendations for each EAA." Indeed, for each EAA, NASEM established a target Eff, estimated based on adequate energy supply, from which recommendations are calculated.

So, using NASEM, nutritionists can estimate EAA supply from a given ration and related Eff for a given production. The objective is to formulate a ration for which the Eff of each EAA will be as close as possible to the "target efficiency." Lapierre points out that NASEM recommendations for all EAA appear in grams per day, not as percentages of MP.

Also, using the Eff of EAA, helps nutritionists evaluate the potential responsiveness of a diet to supplementation with a specific EAA. And finally, a prediction of the Eff of EAA, based on the ratio of EAA:digestible energy supply can be successfully used to predict MPY.

"Optimizing EAA efficiency," Lapierre says, "is key to more manageable ration costs while meeting market demands and addressing consumer concerns."

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