True Value

FROM THE DECEMBER ISSUE: The actual nutritional and economic appraisal of DDGS is more complex than simply measuring profat content.
By Jerry Shurson | November 20, 2018

Ethanol plants have a tremendous opportunity to capture greater economic value from distillers dried grains with solubles. It will require a new way of thinking about what is measured and what those measurements mean for optimizing feeding applications of DDGS in precision animal nutrition feeding programs. There is a huge difference in the chemical content of DDGS measured in the laboratory and the actual nutritional and economic value of DDGS in animal feeds. The gap needs to be bridged between chemical composition data used in the commodity market to establish price, and nutritional composition data used by nutritionists to determine actual feeding and economic value.

Avoid simple measurements
First, it’s important to note that using simple ideas and simple solutions to assess DDGS value has its pitfalls. Oversimplifying can result in inaccuracies. For example, extensive DDGS research has shown that the actual metabolizable energy content of DDGS sources for pigs and poultry is poorly associated with crude fat content alone. Research also shows that color (lightness and yellowness) of DDGS sources is not an accurate predictor of amino acid digestibility. Therefore, nutritional composition of DDGS should be evaluated using a more comprehensive approach to accurately capture true feeding and economic value.

It is also essential for DDGS and corn coproduct producers and marketers to understand the types of nutritional composition data required by animal nutritionists. To do this, coproduct producers and marketers need to consult and work closely with animal nutritionists to provide essential nutritional composition information to their customers. Table 1 (p. 39) provides a summary of most of the essential nutritional composition measures for DDGS usually required by nutritionists. Mycotoxins are a significant concern for nutritionists because the feeding and economic value of DDGS can be significantly diminished when feeding contaminated DDGS sources.

Profat Vs. Actual Nutritional Value
In the current feed ingredient commodity market, the purchase price of an ingredient is based on minimum guarantees for crude protein and crude fat, which are often combined as profat for marketing DDGS. Crude protein and crude fat are components of the proximate analysis scheme that was first developed in 1865 by Henneberg and Stohmann of the Weende Experiment Station in Germany and has been used since to characterize the general composition of animal feed ingredients in the commodity market. However, these measures are grossly inadequate for determining actual nutritional value and are not used in formulating animal diets today. In contrast, animal nutritionists use energy and digestible protein/amino acids, and available or digestible phosphorus to meet the nutritional requirements of dairy, beef, swine and poultry. These nutritional composition measurements are related to the proximate analysis measures, but are quite different when capturing full nutritional and economic value of DDGS.

The key for determining the true nutritional and economic value of DDGS involves relating chemical analysis measures obtained in the laboratory to the digestibility and physiological responses in animals. For example, although we can measure the total oil (crude fat) content in DDGS, it does not mean all of this oil is digestible by the animal or that it contributes to metabolizable energy content. In fact, studies have shown that the digestibility of crude fat among DDGS sources ranges from 53 to 81 percent for swine. This means the combination of oil content and digestibility, along with the fiber and crude protein content and digestibility, determines the actual metabolizable energy content of DDGS.

Crude protein is measured by determining the nitrogen content of a feed ingredient and multiplying the value by 6.25 to estimate the percentage of intact protein and amino acid content. The value of 6.25 is derived from the generalization that the average nitrogen content of an amino acid in intact proteins is 16 percent (1/16 = 6.25 percent). Therefore, crude protein does not actually measure the concentration of intact proteins in a feed ingredient. In fact, several studies have shown that the crude protein content of corn and DDGS is poorly correlated with its amino acid content. Furthermore, the crude protein content of a feed ingredient can be misleading and overestimated if nonprotein nitrogen compounds, such as ammonia or urea, are added to feed ingredients because they contribute nitrogen that is measured in the analysis.

Therefore, although crude protein and crude fat analysis is relatively simple, inexpensive and widely used around the world, animal nutritionists do not use these measures to formulate animal feeds because they are highly inaccurate indicators of utilizable energy and digestible amino acid content of DDGS and other feed ingredients.

Beware the Disconnect
Nutritionists use shadow pricing approaches with least-cost feed formulation software to determine the maximum price for DDGS to enter into the diet formulation based on its energy and digestible nutrient content relative to the cost and nutritional composition of competing ingredients.

To show an example of the inadequacy in using profat for pricing DDGS, actual proximate analysis data for two commercially available DDGS sources (A and B) are shown in Table 2 (above). Most DDGS buyers would select source B because it has greater profat content (34.4 percent) than source A (32.4 percent), assuming source B has greater nutritional and economic value than source A. However, when the actual chemical composition data of these DDGS sources were used as inputs in energy and digestible amino acid prediction equations to provide nutritional composition data, shown in Table 3 (p. 41), DDGS source A actually had greater economic value ($279 per metric ton) than source B ($219 per metric ton) in a growing-finishing swine diet. This is a difference of $60 per metric ton in economic value between these two sources, which may be sold at a similar price. In addition, the actual economic value of both DDGS sources exceeded the spot price of $182 per metric ton (based on the price assumptions for corn and soybean meal at the time of the comparison).

The reasons for the greater economic value of DDGS source A compared with source B is that it contained greater metabolizable energy, net energy and digestible amino acid content, despite having lower profat content. Similar nutritional and economic value differences also exist among DDGS sources for ruminants and poultry. These results provide a real-world example of lost pricing opportunities for DDGS producers and marketers to capture more revenue.

This disconnect between analytical methods and chemical composition measures used to determine price of DDGS and the measurements used to formulate animal diets and determine actual economic value frequently results in the inability of ethanol plants to capture a greater proportion of the true economic value of DDGS. Consequently, DDGS is often marketed at a lower price than the actual economic value it provides in complete animal diets.


Author: Jerry Shurson
Professor, Department of Animal Science,
University of Minnesota
shurs001@umn.edu