Swine & U: Nutritional content of DDGS should be monitored closely

By Jerry Shurson, UMN Swine Nutrition Professor, Department of Animal Science
Originally printed in The LAND - as July 8/July 15, 2022 Swine & U column

Much has changed over the last 20 years in the choices of feed ingredients available and the way swine diets are formulated. One of the most significant changes is the use of corn-derived dried distillers’ grains with solubles (DDGS) in diets for all phases of pork production.

In 1998, when the US ethanol industry was in its infancy, about 1.3 million metric tons (mt) of DDGS were produced, and only about 52, 000 mt (4%) were fed to swine. Today more than 37 million mt of DDGS are produced, of which more than 5 million mt (14%) are being fed to swine domestically and another 13 million mt (35%) are being exported for use primarily in swine and poultry diets in Asia and Latin America.

This dramatic increase in DDGS use in swine diets has occurred for three reasons:

• Existence of an abundant supply of DDGS in major US pork production states
• DDGS have high nutritional and economic value relative to corn and soybean meal
• Extensive research demonstrating that DDGS can be successfully used at high dietary inclusion rates—up to 30%--in all phases of production to achieve optimal performance.

Energy in DDGS

Regarding metabolizable energy (ME) and net energy (NE) for swine, corn DDGS and corn contain, on average, similar ME and NE content. As a result, DDGS prices are generally highly correlated with corn prices in the feed ingredient market.

However, the energy content varies considerably among sources. One of the reasons for the high variability in energy content among DDGS sources is that the majority---more than 90%---of ethanol plants are extracting some of the corn oil prior to manufacturing DDGS. However, research has shown that the oil (crude fat) content of DDGS is a poor single predictor of ME and NE values for swine.

To manage this variability and provide accurate ME and NE estimates of the DDGS sources being used, University of Minnesota swine nutrition researchers (Urriola et al., 2014; and Wu et al., 2016b) have developed and validated prediction equations based on chemical composition.

Commercial companies also use similar prediction equations to help nutritionists and pork producers compare relative economic value and customized energy and nutrient loading values for feed formulation of various DDGS sources. These approaches minimize the risk of overestimating or underestimating energy, digestible amino acid levels and phosphorus content in DDGS as part of a precision swine feeding program.

DDGS provide Protein

Although the protein content of DDGS (27%) is more than three times greater than corn (8%), it is much less than for dehulled, solvent-extracted soybean meal (47%). This is one of the reasons why the DDGS price is less influenced by soybean meal prices than by corn prices. More importantly, the lysine content relative to crude protein content in DDGS (2.97%) is about half the lysine: crude protein in soybean meal (6.20%)

Although the concentrations, balance and digestibility of amino acids in DDGS are inferior to those of soybean meal, DDGS can partially replace soybean meal in swine diets when adequate amounts of crystalline lysine, threonine and tryptophan are supplemented. However, like for energy, the amino acid content and digestibility vary substantially among DDGS sources.

Once again, University of Minnesota researchers (Zeng et al., 2017) have developed prediction equations to accurately estimate the standardized ileal digestibility amino acid content of DDGS sources for swine. This further supports precision swine feeding programs when using DDGS.

More Phosphorus from DDGS than Corn

Another unique and economically valuable nutrition component of DDGS is its relatively high standardized total tract digestible (STTD) phosphorus content (0.47%) compared with corn (0.09%), soybean meal (0.34%), and other grain and grain byproduct sources. Phosphorus is the third most expensive nutritional component in swine diets after energy and amino acids.

As corn is fermented to produce ethanol and DDGS, the phosphorus content is not only concentrated, but much of it is converted to a more digestible form. As a result, substantial amounts of expensive inorganic phosphate supplements can be partially replaced in swine diets when DDGS is added. This not only reduces diet cost, but also reduces the amount of indigestible phosphorus being excreted in manure.

The STTD phosphorus content also varies among DDGS sources, and while prediction equations have been developed to estimate STTD of phosphorus in DDGS for swine, they are not sufficiently accurate. When formulating swine diets, the National Research Council estimate of 65% of STTD of phosphorus in DDGS should be applied to the total phosphorus content of DDGS.

Fine-Tuning DDGS in the Swine Diet

Obtaining accurate estimates of energy and the digestible amino acid and phosphorus content of feed ingredients is one of the most important factors for achieving precision swine nutrition when formulating diets. Using accurate nutritional composition values minimizes the risk of over-feeding or under-feeding energy and nutrients relative to the pig’s requirements. They are also important for capturing the greatest economic value of feed ingredients by minimizing “safety margins” which are frequently used to manage uncertainty in the feed ingredients’ nutritional composition.

Furthermore, if nutritionists have confidence in the energy and digestible amino acid values of the sources of feed ingredients they are using, they are more likely to increase diet inclusion rates if the sources are competitively priced to obtain greater diet cost savings.

Nutrient content varies in all feed ingredients, but some animal nutritionists often complain that the nutrient content among DDGS sources is too variable for them to use compared with other common feed ingredients. While it is well-documented that the energy, nutrient content, and digestibility are variable among DDGS sources, they are no more variable than the nutrient content of other common feed ingredients.

In 2012, Tahir et al. conducted a feed ingredient analysis survey of common feed ingredients used in North America and calculated the coefficient of variation (CV) for several components. Their results showed that the CV of crude protein was less among samples of DDGS (5.4%) than among samples of corn (8.7%) and wheat (19.1%). Furthermore, DDGS had the least variability in neutral detergent fiber (NDF) and phosphorus content compared with corn, soybean meal, wheat, and canola meal. However, as expected, the variability in crude fat content was the greatest among DDGS sources due to the fact that the majority of US ethanol plants partially extract variable amounts of corn oil prior to manufacturing DDGS.

Economic Value of DDGS

Due to the high ME and NE and digestible phosphorus content and relatively high digestible amino acid content of DDGS compared with corn and soybean meal, the economic value of using DDGS in swine diets can be as much as $60-100 per ton greater than the purchase price. Numerous studies have shown that adding high amounts of DDGS—up to 30% in phase 2 and 3 nursery, growing/finishing and lactation diets, and up to 50% in gestation diets---maintains performance comparable to feeding conventional corn/soybean meal diets (Stein and Shurson, 2009).

Significant feed cost reductions have been achieved when using these high DDGS inclusion rates to the point where many large pork producers are attempting to find ways to use even greater amounts (50-60%) in grower/finisher diets. However, to achieve optimal growth performance and carcass composition when feeding diets containing more than 30% DDGS, re-examining the threonine requirements and managing excess leucine relative to isoleucine and valine must be considered.

The Effect of DDGS Fiber and Amino Acids in the Gut

The high fiber content of DDGS may increase the threonine requirement because of increased mucin production in the gastrointestinal tract, which occurs when feeding high fiber diets to pigs. Mucin contains significant amounts of threonine, which is lost and not used for growth. Corn protein in DDGS also contains high amounts of leucine relative the pig’s requirement, and excess leucine reduces the utilization of two other amino acids: valine and isoleucine. Therefore, feeding diets containing high amounts of DDGS may result is suboptimal growth performance if these conditions are not properly managed in diet formulations.

Research is underway to evaluate ways to overcome these challenges and further increase DDGS use in nursery and growing/finishing pig diets.

Author: Jerry Shurson, Professor- Swine Nutrition, University of Minnesota Department of Animal Science. Dr. Shurson can be reached at shurs001@umn.edu.