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Calves and crude protein: Are your calves getting what they need?

Mark Hill, Tana Dennis, and Xavier Suarez-Mena for Progressive Dairyman Published on 31 October 2017

The crude protein (CP) concentrations and sources used in calf starters and growers are frequently questioned and debated today.

Thirty-five (or more) years ago when the understanding of rumen-degradable and undegradable protein was developing, many nutritionists started adding sources of undegradable protein to calf starters and growers, beginning this discussion.



Over this time span, the amount of protein in calf feeds has tended to increase from 16 to 18 percent CP up to 20 to 24 percent CP (as-fed basis).

However, today there is an abundance of research that makes it clear that untreated soybean meal protein is a superior source of protein for calf feeds fed to unweaned and recently weaned calves, up to approximately 4 months of age.

Additionally, the published research shows that 18 percent CP (as-fed basis) is optimum for calf starters fed to calves from birth to approximately 2 months of age, and 15 percent CP (as-fed basis) is optimum for calf growers fed to calves from approximately 2 to 4 months of age.

In 1986, a researcher from Cornell University reviewed the literature on protein sources for calves and found no reason to use sources of undegradable protein in calf starters.

Researchers at the National Institute for Agricultural Research (INRA) and Penn State University each reported that rumen degradation of protein sources are low and increase with age post-weaning.


These observed changes in degradation with age were large and indicate that sources of rumen-undegraded proteins are less needed in young calves than in older animals with more developed rumens.

In addition to no changes in growth measures, researchers from Penn State University reported no difference in the carcass composition from feeding diets with varying concentration of undegraded protein up to 25 weeks of age.

In addition to this research, we have evaluated a number of protein sources for calf grower feeds, including soybean meal (used as a control protein source), soybean meal treated to be less rumen-degradable, blood meal with a commercial methionine source that largely escapes rumen degradation, dried distillers grains with solubles, and some blends of protein sources, and have presented in published research.

The use of treated soybean meal and blood meal with an escape methionine source to increase undegraded protein and provide a good supply of metabolizable amino acids did not improve calf growth compared to soybean meal.

Feeding distillers reduced calf growth compared to soybean meal. In our unpublished research, feeding canola meal and linseed meal reduced calf growth compared to soybean meal.

Energy is frequently more limiting to growth in calf starters and growers than is protein, based on the National Research Council’s calf submodel and considerable recent published research.


Even in trials comparing low-energy, high-fibre and high-energy, low-fibre (high-corn) diets, along with comparisons of soybean meal alone and a soybean meal, blood meal, escape methionine combination, manipulating protein with more undegraded protein sources has not improved calf growth.

The combination of corn and soybean meal offers a good balance of amino acids, is free of many anti-nutritional factors, is low in fibre and is consistently digestible.

A review of protein requirements for calves and heifers in 2013 found that 18 percent CP (as-fed basis) is optimum for calf starters fed to calves from birth to approximately 2 months of age.

Additionally, 15 percent CP (as-fed basis) is optimum for calf growers fed to calves from approximately 2 to 4 months of age. Furthermore, researchers determined that when feeding high levels of high-protein milk replacer, performance was not improved by feeding more protein in the starter.

These optimal protein concentrations and sources were based on both bodyweight and structural growth in expert-reviewed and published research with statistically significant differences in experimental treatments.  end mark

Tana Dennis, Ph.D., and Xavier Suarez-Mena, Ph.D., have calf and heifer technical service responsibilities and are a part of the research team at Provimi.

References omitted but are available upon request. Click here to email an editor. 

Mark Hill
  • Mark Hill

  • Calf and Heifer Technical Services
  • Provimi North America
  • Email Mark Hill

Key take-home points:

  • Soybean meal is the optimal protein source for starters and growers fed to calves less than 4 months of age.

  • Rumen protein sources, even of high-quality, do not increase calf growth.

  • In calves less than 2 months of age, 18 percent crude protein (as-fed basis) is optimal.

  • In calves 2 to 4 months of age, 15 percent crude protein (as-fed basis) is optimal.