By Jerry Shurson, University of Minnesota Department of Animal Science
Numerous studies have been conducted to evaluate the addition of high-oil (> 10% crude fat) and reduced-oil (< 10% crude fat) distiller’s dried grains with solubles sources at inclusion rates up to 60% of the diet, using ME or NE formulation methods, for nursery and growing finishing pigs. We conducted a meta-analysis to summarize the overall growth performance responses of nursery and growing-finishing pigs using data from 26 peer-reviewed references and one thesis published from 2010 to 2017 (Asmus et al, 2014; Benz et al., 2011; Coble et al., 2017; Cromwell et al., 2011; Davis et al., 2015; Duttlinger et al., 2012; Graham et al., 2014a,b,c; Hardman, 2013; Jacela et al., 2011; Jha et al., 2013; Jones et al., 2010; Kerr et al., 2015; Lammers et al., 2015; Lee et al., 2013; Li et al., 2012; McDonnell et al., 2011; Nemechek et al., 2015; Overholt et al., 2016; Pompeu et al., 2013; Salyer et al., 2013; Seabolt et al., 2010; Tsai et al., 2017; Wang et al., 2012; Wu et al., 2016; Ying et al., 2013).
In practice, if accurate energy, digestible amino acid and phosphorus are used in diet formulation, and are specific for the DDGS source being fed, there should be no change in growth performance at relatively high (30%) diet inclusion rates compared with feeding corn-soybean meal diets without DDGS. Although there were fewer observations for growth performance responses of nursery pigs (n = 19) compared with growing-finishing pigs (n = 87), the proportion of responses showing reduced ADG (32%) and Gain:Feed (26%) from feeding DDGS diets was similar in nursery pigs (Table 1) with those for growing-finishing pigs (28 and 26%, respectively).
Installments in the DDGS series
Part 3: Work continues to evaluate performance responses from feeding DDGS
However, the majority of all observations for nursery and growing-finishing pigs, showed no change in average daily gain (71%), average daily feed intake (63%) and Gain:Feed (67%). Therefore, if nursery and growing-finishing diets are formulated using accurate energy and digestible amino acid values for the DDGS source being fed, the majority of studies show that feeding diets containing DDGS provides growth performance responses similar to feeding corn-soybean meal diets the majority of the time.
One of the common misconceptions among swine nutritionists is that reduced-oil (< 10% crude fat) DDGS sources have less energy and feeding value that traditional high-oil DDGS sources. While this is true for some DDGS sources, crude fat content of DDGS is a poor single predictor of energy content among DDGS sources (see Part 2 of this series).
However, if published energy and digestible amino acid prediction equations are used to dynamically estimate these important nutritional components in the DDGS source(s) being fed, and appropriate formulation adjustments are made, there should not be a reduction in growth performance unless there is mycotoxin contamination.
A summary of growth responses from feeding DDGS sources containing high-oil (> 10%) and reduced-oil (< 10%) is shown in Table 2. Overall, the majority of observations in these 27 studies showed an increase or no change in ADG between feeding high-oil (88%) or reduced-oil (64%) DDGS. For ADFI, 82% of the observations showed an increase or no change when feeding high-oil DDGS sources, which was greater than the 68% of responses for reduced-oil DDGS. In contrast, 65% of observations from feeding high-oil DDGS sources showed an increase or no change in Gain:Feed, while 78% of responses showed improved or no change in Gain:Feed when feeding reduced-oil DDGS (Table 2). The majority of responses showing reduced ADG, ADFI, or G:F were due to using inaccurate energy and digestible amino acid values for reduced-oil DDGS sources.
Because of the increased use of high fiber co-products (e.g. DDGS, wheat midds) in swine diets, many swine nutritionists have adopted the use of the net energy system as a more accurate approach to evaluate feed ingredients and formulate swine diets for optimal caloric utilization efficiency compared with the metabolizable energy system. Unfortunately, the NE content and prediction for DDGS sources are not as well defined as for ME content. Although the majority of studies (22 out of 27) in our meta-analysis used the ME system compared with the NE system (Table 3) to formulate DDGS diets, the majority of observations showed similar responses (increase or no change) in ADG (71% for ME, 76% for NE). A greater proportion of observations showed an increase or no change in ADFI using the ME (75%) compared with the NE (62%) system, and all of the Gain:Feed responses resulted in no change when using the NE system compared with 67% of responses showing increases or no change when using the ME system. These results suggest that improved caloric efficiency can be achieved by using accurate NE values for DDGS sources, but more research is needed to develop and validate accurate NE prediction equations for DDGS.
A summary of growth performance responses at various dietary DDGS inclusion rates is shown in Table 4. Negligible effects of feeding diets containing up to 20% on ADG, ADFI, and Gain:Feed have been observed when feeding reduced-oil DDGS to nursery and growing finishing pigs. In fact, the majority of responses for ADG (70%), ADFI (68%), and Gain:Feed (62%) showed no change when feeding diets containing 25 to 30% DDGS. However, although the number of observations were limited (n = 9) when feeding diets containing more than 30% DDGS, about half showed no change in ADG and ADFI, while the other half showed about a 2.4 to 2.8% reduction, respectively. However, the magnitude of these negative responses is small (e.g. 0.90 vs. 0.92 kg/day ADG between DDGS and control diets).
There are several reasons that may explain why feeding diets containing high inclusion rates (> 30%) of DDGS in diets for swine may result in small decreases in growth performance of pigs. First, DDGS has much greater fiber content (35 to 45% NDF) compared with corn and soybean meal. Fiber reduces the ME and NE content of swine diets and also can limit feed intake due to gut fill. As a result, pigs in the nursery and early grower stages may not be able to physically consume enough of a high-fiber diet to meet their energy requirement. Research to improve fiber utilization and ME and NE content of DDGS diets by supplementing diets with feed enzymes, has become one of the most widely researched topics in recent years.
Unfortunately, the use of commercially available carbohydrases and proteases in DDGS diets has not provided consistent or substantial improvements in fiber digestibility and energy utilization by pigs. Secondly, use of accurate ME or NE values for DDGS in diet formulation is essential. Many nutritionists are unaware of the opportunity to use accurate prediction equations to estimate the variable energy (ME) content in DDGS (Urriola et al., 2014), which have been in Part 2 of this series. Use of ME values derived from these equations will ensure optimum diet formulations to minimize suboptimal feed intake and growth. Furthermore, standardized ileal digestibility of amino acids are affected by the fiber concentration in DDGS (Urriola and Stein, 2010), which led us to conduct a meta-analysis of published data to provide accurate prediction equations for dynamically estimate the SID amino acid values of corn DDGS sources based on total amino acid and NDF content (Zeng et al., 2017). In fact, some commercial companies (e.g. Nutriquest, Cargill, and Evonik) offer services to nutritionists to estimate the NE and/or SID of amino acids for DDGS. Therefore, these prediction equations or services should be used by nutritionists to estimate the ME, NE and SID amino acid content among sources of corn DDGS.
Other aspects of DDGS composition that may affect growth performance of pigs when feeding high (> 30%) dietary inclusion rates to pigs have been less studied. Corn DDGS contains high concentrations of fiber, and high dietary fiber increases the threonine requirement of pigs (Zhu et al., 2005). Mathai et al. (2016) showed that the threonine requirement, expressed as a ratio to lysine, was increased for pigs consuming diets with soybean hulls and pea fiber compared with pigs consuming a low fiber diet. Depending on fiber composition, endogenous losses of threonine, and the subsequent requirement of threonine is likely increased when feeding diets containing high concentrations of DDGS (Blank et al., 2012). Based on data from Huang et al. (2017) and Saqui-Salces et al. (2017), and the NRC (2012) model, the estimated threonine endogenous losses (as a % of the requirement) from feeding a high DDGS diets is 7.7% compared to feeding a corn-soybean meal diet (3.2%). As a result, the optimal SID Thr to Lys ratio in DDGS diets may be 61% compared with 59% in corn-soybean meal diets.
In addition to the role of DDGS fiber on endogenous losses of Thr, DDGS also contains a 3.3 times greater concentration of leucine than soybean meal, and the high proportion of leucine relative to isoleucine (1.12×) and valine (1.47×) may result in a deficiency of isoleucine and valine when feeding high (> 30%) DDGS diets with reduced soybean meal content to pigs. These three-branch chain amino acids share the same degradation pathway through the α-keto-acid dehydrogenase complex (BCKDC).
This enzyme is inactivated by a kinase, and its activity is modified by the product of catabolism of leucine (Harris et al., 2004). Consequently, excess intake of leucine increases catabolism of isoleucine and valine (Wiltafsky et al., 2010; Gloaguen et al., 2012). Although Htoo et al. (2017) determined the isoleucine and valine requirements of pigs fed excess leucine (> 160 of SID Leu:Lys), diets containing DDGS have different proportions of leucine to isoleucine and valine, and the validity of using these branch chain amino acid ratios when formulating DDGS diets has not been evaluated in large commercial swine production systems. The effect of excess dietary leucine primarily results in a reduction in feed intake. Excess leucine content in DDGS, and subsequent catabolism of isoleucine and valine can be mitigated by allowing crude protein from soybean meal to meet the amino acid requirement, and avoiding the use of high amounts of synthetic lysine and other amino acids (< 0.15% Lys HCl; Stein and Shurson, 2009).
However, the current relatively low price of synthetic amino acids and DDGS supports reducing the use of soybean meal and increasing the use of synthetic amino acids in swine diets containing > 30% DDGS. Furthermore, the effects of excess dietary leucine on catabolism of isoleucine and valine may also be reduced by adding synthetic isoleucine to the diet to achieve adequate amino acid balance. Studies are underway to evaluate branch chain amino acid balance in diets containing > 30% DDGS for nursery and growing-finishing pigs.