Research Note
NASEM ’21: What’s Missing?
It’s unofficial, but here we are at the fifth anniversary of NASEM 2021, which integrated two decades of new dairy nutrition research to supersede NRC 2001. Practical applications were both “evolutionary” and “revolutionary”, particularly for prediction of dry matter intake (DMI), specific amino acid requirements based on metabolizable protein (MP), and much more.
However, the eighth edition of Nutrient Requirements of Dairy Cattle also broaches new challenges for practicing nutritionists. What do they still need that’s missing?
Virginia Tech’s Dr. Mark Hanigan was a co-author NASEM ’21 and made major contributions to its advance of mathematical models for MP, amino acid utilization, and for modern, high-producing cows.
Building on NASEM ’21, Hanigan says, means further improving the amino acid and energy systems: “We know from several studies that the individual amino acids are not equally digested in the intestine, but there simply was not enough data to define digestion co-efficients for each. We also suspect the amino acid composition of RUP (rumen undegradable protein) is not the same as the feed, but the data were inadequate to represent such changes.”
On the fat side, the system was advanced to represent the supply and milk output of individual fatty acids (FA) as described in the chapter titled Fat.
“We also reflected the effects of individual FA on fat digestibility, and developed a very empirical representation of unsaturated FA effects on milk fat depression.
“However,” Hanigan adds, “there are huge gaps in the FA system including what happens to specific fatty acids in the rumen.
“Failing to represent any of the effects of the microbiota and a myriad of other potential confounding factors limits accuracy and precision of predictions of FA leaving the rumen. We are also missing digestibility co-efficients for individual FA and a representation of the effects of tissue metabolism on FA composition and use. Filling those gaps will be beneficial for diet formulation.”
While NASEM ’21 and the Cornell Net Protein and Carbohydrate System provide nutritionists actionable amino acid (AA) formulation guidance, other researchers acknowledge the need for more work on the synergies between AA and FA. What are the FA requirements for growth, reproduction, and lactation?
Hanigan points to the ongoing fatty acid work of Dr. Adam Lock at Michigan State and Dr. Kevin Harvatine at Pennsylvania State.
Adapted from “Moving from dietary fat to fatty acids”, A. L. Lock et al., 2025
“Of course, we saw tremendous change in dairy cow genomics and performance in the 20 years between the last NRC and NASEM,” Hanigan points out. “Such change is ongoing and, not surprisingly, today’s high-performing Holsteins are genetically more similar. Another twist is that the current beef-on-dairy trend may be further concentrating the on-farm gene pool.”
At present, NASEM ’21 guidance also lacks specific mechanistic data for water-soluble carbohydrates and neutral detergent-soluble fiber, which may have the effect of constraining net energy supply calculations. Future research also may add data for several essential trace minerals, which would further improve dynamic diet formulation.
“Today,” Hanigan notes, “we’re seeing increasingly accurate and impactful diet formulation to support precision feeding on-farm. So while NASEM ’21 addressed many of the NRC’s challenges, there are a number of areas where the available data was inadequate to carry the model forward, and ongoing research continues to expand our knowledge base. So there is no shortage of work to be done.”
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