Nebraska researchers found that roasted soybeans and distiller grains can help address protein limitations in corn silage-based cattle diets.
Corn silage is a common foundation for diets fed to growing cattle, but its relatively low protein quality can make additional supplementation necessary.
Erin Laborie, a Nebraska Extension educator with the University of Nebraska–Lincoln, explains that corn silage typically contains about 6.5% to 8.5% crude protein, with much of that protein classified as rumen degradable protein (RDP).
RDP is broken down in the rumen and used by rumen microbes to produce microbial protein. Rumen undegradable protein (RUP), by contrast, passes through the rumen and is digested in the small intestine.
Along with microbial protein, RUP contributes to metabolizable protein (MP), which cattle need for maintenance, growth and other biological functions. If cattle do not receive enough MP, their growth can be restricted.
Corn silage provides relatively little RUP, with only about 16% of its crude protein classified as RUP, according to the 2022 Nebraska Beef Cattle Report.
Distillers grains are frequently added to silage-based diets because they provide a much higher proportion of RUP, with about 63% of their crude protein in the RUP fraction.
Previous Nebraska research has also documented improved growth performance when distillers grains are included in diets for growing calves.
However, the cost or availability of distillers grains can vary. Soybeans may provide another option because they contain approximately 40% crude protein and also supply dietary fat.
Raw soybeans have relatively low RUP, at about 20% of their crude protein, while roasting can increase the RUP proportion to 50% or more.
Researchers at the University of Nebraska–Lincoln recently evaluated raw, whole and roasted soybeans against modified distillers grains in silage-based diets.
The protein sources were included at 7%, 14%, and 21% of diet dry matter, and the diets were fed to growing heifers for 84 days.
Heifers receiving modified distillers grains had the highest feed intake and weight gains. However, those fed roasted soybeans showed improved feed efficiency.
Across protein sources, the 21% inclusion rate generally produced greater gains and better feed conversion than the 14% rate.
The results indicate that soybeans can provide both protein and fat in growing-cattle diets. Roasted soybeans may offer an advantage because of their higher RUP content, while raw whole soybeans can also be considered when prices and availability make them competitive with distillers grains.
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