Harvesting the entire corn plant at maximum quality and yield provides opportunity to stockpile a considerable amount of forage cost-effectively.
The crude protein content of corn silage is approximately 6.5 to 8.5 percent, which is primarily in the form of rumen-degradable protein (RDP). Rumen-degradable protein is digested in the rumen and utilized by the microbes for protein synthesis.
Rumen-undegradable protein (RUP) escapes rumen degradation and is digested in the small intestine. Corn silage is low in RUP, with approximately 22 percent of the crude protein value consisting of RUP.
The true protein that is absorbed in the small intestine as a combination of microbial crude protein, and RUP is referred to as metabolizable protein (MP). The ruminant animal uses MP to perform metabolic processes involved in maintenance and growth. When MP requirements are not met due to inadequate RUP, growth performance is limited.
Corn silage is a versatile, cost-effective feedstuff that can be used as the main dietary component in growing programs. Staff photo.
In efforts to further evaluate growth performance of calves relative to MP supply, the University of Nebraska – Lincoln conducted a study that fed increasing levels of RUP in corn silage-based growing diets.
Supplemental RUP was included, up to 10 percent of the diet, as a blend of SoyPass (50 percent CP; 75 percent RUP) and Empyreal (75 percent CP; 65 percent RUP).
As the level of supplemental RUP increased in the diet, calves gained more and feed efficiency improved. With the linear increase in gain, it is unclear whether MP requirements were met by supplementing up to 10 percent RUP.
A follow-up study was performed to further evaluate if the growth response would continue once MP requirements were met. Calves were supplemented up to 13 percent RUP as a blend of SoyPass and Empyreal in corn silage-based growing diets. According to the 1996 NRC model, providing 9.75 percent of supplemental RUP would be sufficient to meet the MP requirements of growing calves.
Similar to the observations of other research, average daily gain (ADG) and feed efficiency continued to improve with increasing RUP inclusion. The researchers attributed this increased gain response to the elevated amino acid requirements of growing calves. It was estimated that only the diet with the highest inclusion of supplemental RUP provided adequate amounts of the amino acid, lysine.
While it is unclear whether excess MP would continue to increase growth by meeting lysine requirements or by being utilized as additional energy, it is evident that the addition of RUP in corn silage-based diets improves growth performance of growing calves.
One of the most commonly used feedstuffs that serves as a sufficient source of RUP is distillers grains (DGS). The crude protein value of DGS averages 30 percent with approximately 63 percent being RUP. When DGS is included in a corn silage-based diet, the majority of RUP is coming from corn protein.
Therefore, lysine will likely be the first limiting amino acid and will need to be taken into consideration when formulating diets for growing calves. Depending on whether an operation has access to DGS, it can be an economically favorable source of protein and energy.
Additional feedstuffs relatively high in RUP include corn gluten meal and brewers grains. When comparing various feed ingredients, it is important to evaluate them on a price per unit of nutrient basis.
Conclusion
Corn silage is a versatile, cost-effective feedstuff that can be used as the main dietary component in growing programs. Considering corn silage is relatively low in RUP, the source and amount of supplemental protein are key factors influencing growth. Formulating diets to meet the MP requirements of growing calves is crucial to ensuring growth performance is not compromised.
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