Corn silage is widely used in growing cattle diets, but its relatively low protein concentration and limited rumen-undegradable protein can create nutritional challenges. Research conducted by the University of Nebraska–Lincoln has examined raw and roasted soybeans as potential alternatives to modified distillers grains, offering cattle producers additional options for meeting protein requirements while managing feed costs.
The study compared different protein sources and inclusion levels in silage-based diets for growing heifers over an 84-day feeding period. The findings suggest that both raw, whole soybeans and roasted soybeans can be viable alternatives, depending on their nutritional value, price and availability.
Protein Availability Plays a Key Role in Cattle Growth
Corn silage typically contains approximately 6.5% to 8.5% crude protein, much of which is rumen-degradable protein (RDP). RDP is broken down in the rumen and used by microorganisms to support microbial protein synthesis.
In contrast, rumen-undegradable protein (RUP) escapes degradation in the rumen and is digested in the small intestine. Metabolizable protein (MP), which includes microbial crude protein and digestible RUP, supplies amino acids required for maintenance and growth.
Corn silage contains relatively little RUP, with approximately 16% of its crude protein in this form. Modified distillers grains, which contain a higher proportion of RUP, are frequently included in silage-based diets to help meet the metabolizable protein requirements of growing cattle.
However, when distillers grains become expensive or difficult to obtain, producers may need alternative protein sources to maintain animal performance and control feeding costs.
Raw and Roasted Soybeans Provide Different Benefits
Soybeans contain approximately 40% crude protein and can also supply dietary fat and energy. However, their protein availability differs depending on processing.
Raw, whole soybeans contain relatively low levels of RUP, accounting for approximately 20% of their crude protein. Roasting can increase this proportion to 50% or more, allowing a greater share of the protein to bypass rumen degradation and become available for digestion in the small intestine.
These differences make roasted soybeans a potential option for diets where additional RUP is needed. Nevertheless, the overall value of each ingredient depends on the complete ration, energy supply, digestibility and cost.
University Study Compares Three Protein Sources
Researchers at the University of Nebraska–Lincoln compared modified distillers grains with raw, whole soybeans and roasted soybeans in corn silage-based growing diets.
The ingredients were evaluated at three inclusion levels: 7%, 14% and 21% of diet dry matter. All experimental diets were formulated to meet or exceed the metabolizable protein requirements of growing heifers.
The 84-day study assessed feed intake, weight gain, feed efficiency and ending body weight, providing insights into how protein source and inclusion rate influence growing cattle performance.
Modified Distillers Grains Deliver Higher Intake and Gains
Heifers receiving modified distillers grains recorded the greatest feed intake and weight gains among the protein sources evaluated. However, feed efficiency improved in heifers fed roasted soybeans, indicating that roasted soybeans may offer advantages in converting feed into body weight.
The inclusion rate also influenced performance. Across the evaluated protein sources, weight gains were greatest when the ingredient was included at 21% of diet dry matter. Feed conversion generally improved at this inclusion level compared with 14%.
Ending body weight increased linearly with higher inclusion levels of modified distillers grains and raw, whole soybeans. Because all diets met protein requirements, researchers suggested that the response to higher inclusion levels may have been driven partly by increased energy supply rather than protein alone.
These findings highlight the importance of evaluating complete diet composition instead of selecting feed ingredients solely on their crude protein concentration.
Feed Costs and Availability Determine Practical Value
Soybeans can provide both protein and fat in growing cattle diets, making them useful ingredients in silage-based feeding programs. Roasted soybeans offer a higher RUP concentration than raw, whole soybeans and may improve feed efficiency under suitable dietary conditions.
Nevertheless, modified distillers grains supported the greatest intake and weight gains in the study. Soybeans should therefore be considered alternative ingredients rather than universally superior replacements.
For cattle producers, the most suitable option will depend on local ingredient prices, processing costs, feed availability and animal performance targets. A balanced ration should account for metabolizable protein, energy, fat and other nutritional requirements.
Overall, the University of Nebraska–Lincoln study indicates that raw and roasted soybeans can provide practical alternatives to modified distillers grains in growing cattle diets when appropriately formulated. Comparing their costs and nutritional contributions may help producers develop flexible feeding strategies while supporting cattle growth and efficient feed utilization.
