Many of our discussions over environmental stewardship and nutrient management in confined animal feeding operations are focused on managing the excretory products of an operation.
Therefore, we often overlook the diet ingredients and diet nutrient concentrations as essential components of nutrient management. In many cases diet formulation and ingredient selection is based on factors, such as ingredient cost, cost of gain and feed conversion. Therefore, the challenge associated with the bunk side of nutrient management is developing cost-effective rations that balance animal performance and environmental stewardship.
The expansion of the ethanol industry and increase in the utilization of distillers byproducts in the livestock industry has made this challenge even more difficult. Wet distillers grain (WDGS) contains approximately 3.2 times the amount of nitrogen and 2.7 times more phosphorous than corn. (See Table 1*). The greater nitrogen and phosphorous concentration in WDGS is due to the conversion of starch within the grain to alcohol and carbon dioxide. The removal of the starch effectively concentrates the other components of the grain within distillers grains.
The use of WDGS and other grain byproducts is becoming more common in cattle feeding operations. A survey conducted by the National Agricultural Statistics Service that encompassed 9,400 livestock producers in 13 states reported that 36 percent of beef cattle feeding operations were utilizing distillers grains or corn gluten feed in their operations. Additionally, a survey of feedlot consulting nutritionists reported that 82.8 percent of their clients were using grain byproducts (WDGS, dried distillers grains, wet corn gluten feed or dry corn gluten feed) in finishing rations.
Historically, a conventional feedlot finishing diet consisted of approximately 80 to 90 percent grain (corn or sorghum) and 5 to 10 percent roughage (alfalfa or silage). This conventional finishing diet would have contained approximately 2.1 percent nitrogen and 0.3 percent phosphorous. However, today the composition of feedlot finishing diet is becoming more reflective of the increased availability of grain byproducts and now consists of approximately 60 to 65 percent grain, 15 to 20 percent byproducts and 5 to 10 percent roughage on a dry basis.
The diets used in a feedlot study at Kansas State University demonstrate the impacts of different levels of WDGS inclusion on total nitrogen and phosphorous content of the diet. (See Table 2*). The percentage of nitrogen increases from 2.24 percent in the diet containing 0 percent WDGS to 2.70 percent in the diet containing 30 percent WDGS. The level of phosphorous also increases from 0.28 to 0.50 percent in the 0 and 30 percent diets, respectively.
When corn is replaced with WDGS in a ration, an ingredient containing 1.50 percent nitrogen and 0.32 percent phosphorous is substituted with a feedstuff containing 4.77 percent nitrogen and 0.85 percent phosphorous. Ingredient selection and diet nutrient content directly influence how we manage the excretory products produced from an operation. Therefore, the bunk side of nutrient management should not be overlooked, especially if the operation is considering utilizing byproducts such as WDGS in the ration. PD
References and tables omitted but are available upon request at editor@progressivedairy.com
Justin Waggoner
Extension Beef Systems Specialist
Kansas State University
jwaggon@k-state.edu
