Beef Producers Advised to Rethink Protein Needs for Calves

UNL Professor Explains Why Crude Protein System Doesn't Work Well for Growing Calves

Mar. 18, 2026 at 6:11am

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Dr. Mary Drewnoski, a professor and beef systems extension specialist at the University of Nebraska-Lincoln, is advising beef producers to reconsider how they approach protein needs for growing calves. Her research shows the traditional crude protein system does not effectively meet the nutritional requirements of calves, especially lighter-weight ones.

Why it matters

Properly balancing the protein and energy needs of growing calves is crucial for optimizing their weight gain and overall health. Drewnoski's research highlights how the crude protein system can fall short, leading to underperformance, and provides guidance on alternative approaches that could help beef producers improve calf growth and efficiency.

The details

Drewnoski's research involved 500-pound steer calves grazing corn residue, with one group receiving a supplement of 5% urea and another group getting distillers grains (DDGs). While the two supplement groups had the same crude protein levels, the DDGs group gained 1.32 pounds per day compared to only 0.5 pounds per day for the urea group. The difference lies in how the rumen processes the two protein sources - urea is rumen-degradable, while DDGs contain rumen-undegradable protein that can be directly utilized by the animal.

  • The UNL research program involving the 500-pound calves took place over an unspecified period of time.

The players

Dr. Mary Drewnoski

A professor and beef systems extension specialist at the University of Nebraska-Lincoln who conducted research on calf protein needs.

University of Nebraska-Lincoln (UNL)

The university where Dr. Drewnoski is a professor and where the research on calf protein needs was conducted.

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What they’re saying

“Many would guess that the corn-urea group performance would be less than the DDGs group. And they would be correct. Performance on corn-urea was only about 1/2 pound per-day gain. The DDGs group gained 1.32 pounds per day. If you look at the difference between the two – crude protein the same, energy the same – what's going on?”

— Dr. Mary Drewnoski, Professor and Beef Systems Extension Specialist, University of Nebraska-Lincoln

“If we continue to feed high-quality alfalfa hay, dairy quality, which is 24 to 25 percent crude protein, and expect high rates of gain in calves, what may happen is that there's actually not enough energy to make use of all that protein, so we don't get as high a gain as expected. If we provide a bit more energy, such as corn, it will boost performance.”

— Dr. Mary Drewnoski, Professor and Beef Systems Extension Specialist, University of Nebraska-Lincoln

What’s next

Drewnoski recommends that beef producers test the quality of their forage sources, especially alfalfa hay, to ensure they are providing the right balance of protein and energy to optimize calf growth and performance.

The takeaway

Drewnoski's research highlights the limitations of the traditional crude protein system for meeting the nutritional needs of growing calves, especially lighter-weight ones. By understanding the differences between rumen-degradable and rumen-undegradable protein sources, beef producers can make more informed decisions to support optimal calf growth and development.