NASEM 2021 explained: the new dairy nutrition rulebook in plain language

NASEM stands for the National Academies of Sciences, Engineering, and Medicine. Its book Nutrient Requirements of Dairy Cattle (8th edition, 2021) is the reference many nutritionists and ration programs worldwide use to calculate what cows need. It replaced the NRC 2001 edition after twenty years of new research.

Think of it as a recipe calculator

You enter the cow (weight, milk, stage of lactation) and the feeds. NASEM estimates how much energy, protein, amino acids, minerals and vitamins she needs, and how much the ration supplies.

What changed — simply

• Energy: feeds are less digestible when cows eat more, and NASEM now accounts for this.
• Starch and fibre digestibility are calculated more realistically.
• Protein: requirements are expressed per essential amino acid, so rations can contain less crude protein.
• Minerals: updated absorption values, generally leading to lower mineral feeding.
• Calves and heifers: a much-improved section on milk feeding and growth.
• Water and environment are discussed more fully.

What it means for you

NASEM is a tool, not a magic answer. Its predictions are only as good as the feed analyses and intake data you feed into it — which is why sampling and measuring intake matter. Ask your nutritionist which model version they use.