NASCalf Amino Acids

Hello, and welcome to this NASCalf tutorial. In this video, we’ll look at how NASCalf models protein and amino acid nutrition in young calves.

Protein nutrition in calves is still not fully understood, particularly the flow of metabolizable protein and amino acids from dietary and microbial sources. Early in life, the calf functions essentially as a monogastric, with most amino acids coming from milk that bypasses the rumen and is digested in the abomasum. As the rumen develops, this shifts, and an increasing proportion of amino acids reaching the small intestine is derived from microbial protein—primarily bacteria, and eventually protozoa once a stable rumen environment is established. NASCalf models this transition using assumptions about changing contributions of microbial protein and rumen undegradable protein, based on the 2021 NASEM publication.

Amino acid requirements in the model are calculated using a factorial approach, accounting for both maintenance and growth. These calculations follow NASEM (2021) guidelines and are based on empty body weight gain and the composition of that gain. To help evaluate these dynamics, NASCalf provides two diagnostic tools. The first is the Protein Report, which summarizes maintenance requirements—such as endogenous urinary losses and metabolic fecal nitrogen—and estimates amino acid needs. It also shows metabolizable protein supply from rumen undegraded protein and microbial sources, separated by liquids, grains, and forages.

The second tool is the Supply and Requirement window, which compares amino acid supply to requirements. This includes contributions from liquids, dry feeds, rumen undegraded protein, and microbial protein, along with their respective amino acid profiles. The model then calculates total supply and compares it to requirements for maintenance and growth, reporting any deficits or excesses.

It’s important to recognize that these calculations rely on a number of assumptions due to limited published data. As a result, they should be viewed as estimates that are directionally useful, rather than precise predictors of amino acid limitations. However, they provide a valuable framework for understanding protein nutrition during the calf’s transition from a monogastric to a functional ruminant.

Thanks for watching, and be sure to explore other NASCalf tutorials to get the most out of the program.