By Jerry Shurson, Pedro Urriola, Zhikai Zeng and Jae Cheol Jang, University of Minnesota Department of Animal Science
As we described in the previous article of this series (Part 5 — Reaching an understanding of fiber characteristics of corn DDGS), the relatively high fiber content of distiller’s dried grains with solubles significantly reduces the net energy to gross energy ratio in corn DDGS for swine.
As a result, there has been tremendous interest in supplementing DDGS diets with various commercially available carbohydrases and proteases to increase the NE:GE in corn DDGS. Świątkiewicz et al. (2015) summarized responses from adding various enzymes to corn DDGS diets for swine (Table 1). In general, the majority of these studies showed improvements in nutrient digestibility when enzymes were added to corn DDGS diets, but these improvements were often not associated with improvements in growth performance. Several studies summarized in this review evaluated only phytase responses, and not combinations of phytases with carbohydrases and proteases.
Furthermore, some studies in the Świątkiewicz et al. (2015) review were excluded from Table 1 because they were comparisons with wheat- or wheat-corn blends of DDGS, and were not representative of responses to adding enzymes to corn DDGS diets due to different fiber and nutrient characteristics. However, several studies have been published since the Świątkiewicz et al. (2015) review.
To provide a more comprehensive analysis and summary of the overall effects of adding various types and combinations of feed enzymes to corn DDGS diets on growth performance of nursery, growing and finishing pigs, as well as energy, nutrient and NSP digestibility, we conducted a meta-analysis using data reported from 52 published studies since 2000 (Agyekum et al., 2016; Agyekum et al., 2012; Ao et al., 2011; Asmus et al., 2012; Barnes et al., 2011; Benz et al., 2009; Brooks et al., 2009; Carr et al., 2014; Chen et al., 2016; Cho et al., 2016; de Vries et al., 2014; de Vries et al., 2013; Feoli et al., 2012; Graham et al., 2012; Han et al., 2017; Jacela et al., 2010; Jakobsen et al., 2015; Jang et al., 2017; Jones et al., 2015; Jones et al., 2010; Kerr et al., 2013; Kiarie et al., 2016; Kiarie et al., 2012; Kim et al., 2006; Kim et al., 2004; Kim et al., 2003; Koo et al., 2017; Lan et al., 2017; Lee et al., 2011; Lenehan et al., 2003; Li et al., 2012; Moran et al., 2016; Ndou et al., 2015; Passos et al., 2015; Pedersen et al., 2014; Petty et al., 2002; Ragland et al., 2008; Sandberg et al., 2016; Shrestha, 2012; Stephenson, et al., 2014; Świątkiewicz et al., 2013a; Tactacan et al., 2016; Tsai et al., 2017; Upadhaya et al., 2016; Wang et al., 2011; Widyaratne et al., 2009; Wiseman et al., 2017; Woyengo et al., 2015; Xuan et al., 2001; Yanez et al., 2011; Yoon et al., 2010; Zuo et al., 2015). A summary of the overall effects of adding various types and combinations of feed enzymes to corn-soybean meal-DDGS diets on pig growth performance as well as energy, nutrient and NSP digestibility are shown in Table 2, 3 and 4.
Installments in the DDGS series
Part 1: 20 years of DDGS lessons in pig diets
Part 2: Varied energy and digestible amino acids levels in DDGS manageable
Part 3: Work continues to evaluate performance responses from feeding DDGS
Part 4: Managing carcass yield, pork fat quality when feeding corn DDGS
Part 5: Reaching an understanding of fiber characteristics of corn DDGS
Part 6: Enzymes, pre-treatment improve fiber and nutrient digestibility
Part 7: DDGS show greater antioxidant capacity than in corn grain
Regardless of types of enzymes supplemented in corn-soybean meal and CSD diets, average daily gain and G:F were slightly improved in all cases (Table 2). However, overall average daily feed intake responses were slightly reduced in both CS (-0.63%) and CSD (-0.19%) diets, but varied from -8.85% in CSD diets supplemented with mannanase to +1.62% in CS diets supplemented with carbohydrases plus proteases (Table 2). It is unclear why some types of enzymes appear to reduce ADFI in both CS and CSD diets, but for the CSD diets supplemented with mannanase, only two comparisons were in the data set which may not adequately characterize this ADFI response.
The overall improvement in ADG from feed enzyme supplementation in CSD diets was slightly greater (+2.67%) than in CS diets (+1.94%), but there was a slightly greater overall improvement in G:F from enzyme supplementation in CS diets (+2.65%) compared with feeding CSD diets (+1.87%; Table 2). The slightly greater G:F improvement from adding enzymes to CS diets appears to be partially due to the slightly greater reduction in ADFI in CS diets compared with the CSD diets. It is interesting that the addition of proteases (+7.32%) to CS diets resulted in the greatest improvement in ADG among all enzyme comparisons, followed by carbohydrases plus proteases (+3.16%), and xylanases (+3.14%), while xylanase (+3.64%), mannanase (+3.62%) additions resulted in the greatest improvement in ADG in CSD diets, followed by proteases (+2.67%). Similarly, the greatest improvement in G:F in CS diets was from the addition of proteases (+7.46%), but mannanase (+13.68%) supplementation in CSD diets provided even greater improvement in G:F.
However, it is important to note that the improvements in ADG and G:F from adding proteases to CS diets occurred in nursery pigs (initial body weight of 6.3 to 8.3 kilograms, diets were fed from 12 to 42 days), while the improvement in ADG and G:F from adding proteases to CSD diets occurred in growing-finishing pigs (initial body weight of 25-50 kilograms; final body weight of 114-131 kilograms), and were based on only three comparisons. Because no studies reported ADG and G:F responses for protease supplementation in CS diets for growing-finishing pigs, and CSD diets for nursery pigs, it is difficult to compare responses between CS and CSD diets and different growth phases. However, these data suggest that the addition of mannanase and xylanase to CSD diets can be effective for improving ADG and G:F of nursery and growing-finishing pigs compared with feeding diets without these types of feed enzymes.
These growth performance improvements appear to have occurred despite the minimal positive effects of various feed enzymes on dry matter and gross energy digestibility, and negative effects on nitrogen (crude protein) and ether extract (crude fat) digestibility (Table 3). However, adding various enzymes to CSD diets appear to substantially improve total NSP and insoluble NSP digestibility (Table 4).
Nutritionists can use the results from this meta-analysis to determine if the magnitude of improvement in economically important growth performance responses is great enough to justify the cost of adding various types of feed enzymes to DDGS diets for swine. The type of carbohydrase, protease or xylanase should be considered in this evaluation to determine the likelihood of achieving these responses under commercial conditions.
Another approach to increase the NE:GE in corn DDGS is to use various processing and pre-treatment methods to degrade fiber and enhance energy and nutrient digestibility. For example, simply grinding corn DDGS to a smaller average particle size can increase ME content of DDGS by 13.5 kilocalories per kilogram (dry matter basis), for each 25-micron reduction (Liu et al., 2012). Although grinding has been shown to be effective for improving the ME content of DDGS, grinding and pelleting do not substantially degrade NSP structures (de Vries et al., 2012). Therefore, most of the research to evaluate potential feed processing methods of DDGS, have focused on pre- or post-treatment approaches using chemical or physical treatments to degrade the fiber structure of DDGS.
Hydrothermal pre-treatments using acid catalysts have been shown to be effective in degrading lignocellulosic material (Sun and Cheng, 2002), but they can cause protein damage and increase acid or mineral content (van den Borne et al., 2012). In contrast, the use of mild acid (maleic acid) hydrothermal treatment has been shown to increase solubilization of NSP in DDGS (de Vries et al., 2013). However, although acid extrusion facilitated more rapid degradation of NSP, and shifted fermentation to more proximal locations in the gastrointestinal tract, more than 35% of NSP in DDGS were not degraded (de Vries et al., 2014). As a result, these authors suggested that enzymes and other process technologies may be more effective if ester-linked acetyl, feroyl or coumaroyl groups of the fiber structure are targeted. In cereal grains, ferulic acid, p-coumaric acid and sinapic acid are involved in coupling of arabinoxylans, cell wall trapped protein and lignin like polymers (Ralph et al., 1995; Bunzel et al., 2004; Piber and Koehler, 2005). Ferulic acid and its derivatives are the most important cross-linkages in grain cell walls, and are bound to arabinoxylans and pectins (Bunzel, 2010). Dimers, trimmers and oligomers of ferulic acid cross-link with two or more polysaccharide chains to strengthen the cell wall, but impair enzymatic degradation (Grabber et al., 1998a,b) leading to reduced fiber digestibility in DDGS.
In fact, Pedersen et al. (2015) reported that the concentrations of ferulic acid dimers and trimmers were five to six times greater in corn DDGS than in wheat or grain blends of DDGS. These results indicate that the ferulic acid cross-links in the corn fiber cell wall do not appear to be modified during fermentation and production of DDGS.
Ammonia fiber expansion is an alkaline pre-treatment technology that disrupts the crystalline structure of cellulose and significantly enhances enzymatic digestibility from fiber rich biomass (Mosier et al., 2005; Gao et al., 2010). In ruminants, AFEX-treated forages were reported to have greater NDF digestibility when evaluated in vitro with rumen inoculum (Bals et al., 2010). This research group also attempted to optimize AFEX pre-treatment conditions in corn DDGS, and reported that almost all of the cellulose in DDGS was degraded after 72 hours of enzymatic hydrolysis and released 190 grams of glucose dry biomass (Bals et al., 2006). Corn DDGS contains 5.8 % cellulose and accounts for about 23.3% of total NSP (Jaworski et al., 2015). Therefore, if cellulose in DDGS was hydrolyzed before entering the lower gastrointestinal tract of pigs, it may contribute about 242 kilocalories per kilogram DE (Noblet and van Milgen, 2004) to the energy value of DDGS. More importantly, the proportion of arabinoxylans imbedded in cellulose may be exposed and more accessible to degradation from exogenous enzymes, bacteria, organic acids and their combination.
Newer methods to improve digestibility of nutrients and energy in DDGS have been evaluated using whole stillage, which is the wet portion of the residual grain before drying. Pretreatment of whole stillage increased in vitro digestibility of dry matter by 11% when treated with acid (10 grams per liter), and by 15% when treated with ammonia (Zagnaro et al., 2018). These researchers also showed that adding a cocktail of carbohydrase enzymes increased in vitro digestibility of dry matter independently of pre-treatment. The results from this study suggest that pre-digesting whole stillage in an ethanol facility may be effective in improve the nutritional value of corn DDGS.
Results from these studies suggest that the chemical and physical structure of fiber in DDGS is complex, and practical pre-treatment methods need to be developed to significantly degrade the fiber structure in corn DDGS to make it more accessible to endogenous and exogenous enzymes to increase energy and nutrient utilization in swine.
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