Over the past eight years, one significant change that has occurred in ethanol coproduct production has been the extraction of distillers corn oil (DCO) in dry-grind ethanol plants, with approximately 85% of all U.S. ethanol plants extracting it. This has led to highly variable oil (4.5% to 13% crude fat) and nutrient content among distillers dried grains with solubles sources.
Since DDGS is primarily an energy source in swine diets, partial removal of oil caused nutritionists to expect that the metabolizable energy (ME) and net energy (NE) content might be reduced due to reduced-oil (RO) content. The challenge for nutritionists who formulate diets for pork producers is to manage variability in ME and nutrient content among RO-DDGS sources and to find ways to accurately predict ME content.
Accurate estimation of ME values for RO-DDGS sources is important for accurate and precise diet formulation and optimizing the nutritional and economic value of RO-DDGS in swine diets. Several recent studies have been conducted to develop digestible energy (DE) and ME prediction equations. A Minnesota-based research team has further evaluated the accuracy and applicability of these equations using validation studies to assess the ME content of DDGS sources with oil content ranging from less than 5% to greater than 10%.
These equations were put to the test by comparing growth performance and carcass composition of growing and finishing pigs substituting corn-soybean meal diets with 40% DDGS from three sources of similar predicted ME, but different in 6%, 10% and 14% EE (ether extract) content. Pigs fed low-oil (6% EE) DDGS grew 0.356 pound for each pound of feed consumed, compared with 0.368 pound in pigs fed the corn-soybean meal diet. This observation suggests that current equations overestimate the ME content in DDGS with less than 6% EE, but are accurate for RO-DDGS with EE greater than 6%.
It has been well documented that feeding corn-soybean meal diets containing increasing dietary levels of DDGS to growing-finishing pigs results in reduced pork-fat firmness. Numerous regression equations have been developed to predict dietary iodine value (IV) in jowl, backfat or belly fat based on IV product (IVP) of diets, linoleic acid intake and percentage of DDGS in the diet. Researchers compared the precision and accuracy of predicting backfat IV using these equations and found that the Paulk et al (2015) equation resulted in the best prediction with the least error and bias. However, the magnitude of the prediction error and bias of these equations needs to be reduced to achieve more predictable carcass fat IV responses when feeding DDGS diets to growing-finishing pigs.
The importance of neutral detergent fiber (NDF) in the DE and ME prediction equations, along with the relatively high fiber content in DDGS, has led the University of Minnesota research team to initiate several studies to better understand the effects of feeding high-fiber diets to growing pigs.
One reason these prediction equations are less accurate in correctly estimating ME or NE content in RO-DDGS with less than 6% oil is that a significant amount of energy can be derived from fiber. The role of various sources and amounts of dietary fiber contribution to ME and gut health is poorly understood. It has been observed that feeding various sources of fiber modifies gut morphology, cell proliferation, immunity and digesta transit time. These changes affect efficiency of feed utilization and carcass yield, but are not predicted using current analytical measurements (e.g., crude fiber, neutral detergent fiber, total dietary fiber).
Therefore, a better understanding of the physiological mechanisms of fiber from various sources, including RO-DDGS, will allow researchers to develop more effective tools to increase caloric and nutritional efficiency, as well as growth performance of pigs when fed high-fiber diets.
Distillers coproducts continue to be a valuable source of energy, digestible amino acids and digestible phosphorus for cost-effective feeding programs in pork production. Variability among sources of RO-DDGS in nutrient concentration, digestibility and subsequent nutritional value to livestock will continue to increase. The resulting variability can be managed using research and mathematical models that are developed and validated.
For further information, contact Gerald Shurson at 612-624-2764 or [email protected]. References: Anderson et al (2012). J Anim. Sci. 90:1242-1254. Paulk et al (2015). J. Anim. Sci. 93:1666-78.