Fiber concentration of ingredients should be considered as greater concentrations can decrease the digestibility of energy through decreased lipid digestibility (Wilfart et al., 2007). Although, the negative relationship between energy digestion and fiber inclusion may be improved with increasing pig age and weight due to increased retention time through the digestive process. This allows for greater inclusion rates of fiber in grow-finish diets (Le Goff et al., 2002). However, the type of fiber utilized in diet formulation should also be considered as this can affect nutrient digestibility to different degrees. While both insoluble and soluble fiber decrease energy digestibility, inclusion of moderate to high levels of insoluble fiber (i.e., wheat middlings and dried distillers grains with solubles [DDGs]) ingredients decrease the digestibility of energy toa greater extent than soluble fiber ingredients (i.e., sugar beet pulp and citrus pulp; Owusu-Asiedu et al., 2006).
The effects of fiber utilization on grow-finish growth performance should be considered when evaluating the dietary energy level and use of high-fiber ingredients in diet formulation. It has been reported that including high levels of DDGS in grow-finishing diets does not affect growth performance compared to a corn-soybean meal diet, but reductions in performance have been observed in other studies (Linneen et al., 2008; Nemechek et al., 2015; Coble et al., 2017). The inconsistency in the response to DDGS could be attributed to the large variability in its nutrient composition. Dried distillers grains with solubles commonly have greater concentrations of crude fat, CP, and fiber than corn. The energy content varies with changes in oil and fiber components (Peterson, 2007; Graham et al., 2014). Graham et al. (2014) developed an equation based on oil content of DDGs sources to predict their NE content (Figure 2). Therefore, NE values should be used to provide more accuracy in diet formulation and an equation is available to aid in prediction of NE values of DDGs sources.
Fiber Withdrawal Strategies
Because reductions in performance can be observed when feed contains high fiber ingredients, nutritional strategies can be developed to alleviate these negative responses. An effective strategy that has been utilized is switching from high fiber diets to low fiber diets (fiber withdrawal) shortly before marketing. Withdrawing high fiber ingredients from the diet and switching to a corn-soybean meal diet has been observed as an effective tool at recapturing growth performance and carcass yield losses before marketing (Asmus et al., 2014; Graham et al., 2014; Soto et al., 2017). The benefits from the withdrawal strategy can be attributed to the energy and fiber relationship on feed intake. Feeding high fiber ingredients increases gut fill due to the increased dietary bulk density and can limit energy intake (Whittemore, 2001). Furthermore, reduced carcass yield is observed when high fibrous diets are fed throughout the grow-finish phase as the intestinal contents at harvest are increased (Asmus et al., 2014; Coble et al., 2017). By switching from a high fiber diet to corn-soybean meal diets, carcass yield can be improved. This diet switch should be done with the last diet before final marketing. However, the response to fiber withdrawal depends on the level of fiber in the diet and duration of the withdrawal (Lerner et al., 2018). An economic evaluation must be conducted to determine if withdrawing high fiber ingredients from the diet before market will optimize economic success.
The inclusion of high fiber ingredients should be considered in growing-finishing pig diets as they can help alleviate high feed costs; however, the negative effects on growth performance as well as carcass performance should be considered. An economic evaluation should be conducted when using high fiber ingredients in diet formulation to determine appropriate inclusion rates and feeding duration.