Rumen available protein is the portion of feed protein that rumen microbes can break down and use. In feedlot diets, it is often discussed as rumen degradable protein. The portion that escapes breakdown in the rumen is called rumen undegradable protein, or bypass protein.
Balancing these two protein fractions matters because cattle need both:
- An active rumen microbial population to support fermentation and fiber digestion
- Adequate metabolizable protein reaching the small intestine
Rumen available protein is especially important when feeding diets that contain high-moisture corn from silage, earlage, or wet corn. From a practical standpoint, the goal is to feed the starch-digesting microbes in the rumen so cattle can more fully utilize high-moisture corn.
How Common Protein Sources Function in the Rumen
Distillers grains and soybean meal are both valuable protein sources, but they behave differently in the rumen:
- Distillers grains typically provide a strong supply of bypass protein, with a smaller yet useful rumen available fraction.
- Soybean meal generally supplies more rumen available protein than distillers grains.
- Soybean meal can be useful when a ration needs a readily available natural protein source to support rumen microbes, especially in diets with larger amounts of high-moisture corn.
Alfalfa hay contributes rumen available protein along with effective fiber. This can help keep cattle on feed, especially during stress situations. While alfalfa is not usually the most concentrated protein source and its inclusion in finishing diets is limited, its protein is generally quite degradable and can complement high-moisture corn diets that need both roughage and rumen nitrogen. Its value in finishing diets depends heavily on forage quality.
Urea is a non-protein nitrogen source that is considered fully rumen available. It must be used carefully because it supplies nitrogen without supplying true protein, energy, or fiber. Urea can be an effective way to supply rumen available protein in high-moisture corn diets.
Producer Takeaways
- High-moisture corn is a valuable ingredient in Iowa feedlot diets.
- Rumen available protein helps feed the microbes that digest starch and support rumen function.
- Different protein sources contribute differently: distillers grains provide more bypass protein, while soybean meal and alfalfa can provide more rumen available protein.
- Urea is fully rumen available but should be used carefully because it provides nitrogen only.
We would like to help you make the most of this homegrown ingredient. Call your FCS feed representative to learn more!