Feeding high fiber feed ingredients (e.g. wheat middlings and corn distillers dried grains with solubles) significantly decreases feed efficiency of pigs. However, the addition of carbohydrase enzymes to feed offer the potential to partially overcome these reductions in feed efficiency. However, results from feeding experiments of high fiber diets supplemented with carbohydrase enzymes (including NPB projects #13-158, 13-191, and 14-234) are have been inconsistent with generally poor effectiveness. One potential reason for the ineffectiveness of carbohydrases, is that there are multiple types of these products, produced by multiple suppliers, and multiple target substrates where upon specific enzymes work. There are no systematic reviews or experiments that allow for comparing products and enzyme activity of the commercial carbohydrases. Likewise, the relative effectiveness of carbohydrase enzymes on growth performance, nutrient digestibility, and gut physiology effects are unknown. We speculate that the overall impact of carbohydrase enzymes on feed efficiency of growing pigs can be described by 1) an improvement of energy and nutrient digestibility or ‘nutrient uplift’or by 2) an improvement in energy and nutrient utilization, or a ‘non-nutrient’ effect. Results from previous UMN projects (NPB 13-014) have shown that use of an in vitro digestibility and gas production system can provide a reasonable estimates of DM and GE digestibility of high fiber feed ingredients. This in vitro system allowed us to compare digestibility values of 11 different carbohydrase enzymes in fiber from wheat middlings and corn DDGS. Results from these studies suggest that of the 11 of the most common carbohydrase enzymes available in the U.S. market, none of them have a measurable effect on digestibility of DM and GE when added to corn DDGS, and minimal improvements when added to wheat middlings. However, despite of the limited ability of these enzymes to improve digestibility of DM and GE, pigs fed wheat middlings and carbohydrase enzymes had greater feed intake than pigs fed the same diets not supplemented with enzymes. The reason for this improvement in feed intake is not clear, but it may be related to the fact that feeding carbohydrase enzymes modifies the composition and physico-chemical characteristics of digesta in the gastrointestinal tract. Specifically, enzymes increased the release of xylose monosaccharides into the liquid portion of the jejunum and ileum contents. These modifications of fiber in the presence of these carbohydrases also decreased the force required to stir jejunal and ileal contents. In addition, adding carbohydrase enzymes to these diets also modified the immune response of pigs, which varied along different parts of the gastrointestinal tract and between the types of enzyme substrates in the diets (wheat middlings vs. corn DDGS). These observations are in agreement with our previous NPB reports (13-014), where we observed that fiber has a significant impact on gut cell proliferation, differentiation, and immune function. However, the implications of these observations on other factors such as resistance to infections and other stressors are yet to be determined. In conclusion, feeding enzymes may modify the gastrointestinal mileu and improve feed efficiency of pigs fed fibrous feed ingredients, but not by improving nutrient digestibility, but rather by modifications of gut function. The practical application and consistency of effects need to be further evaluated by conducting studies that help us understand how the physical structure of fiber in DDGS is related to effectiveness of these enzymes. Knowing this, it may be possible to design enzymes that will have greater effectiveness for increasing energy and nutrient digestibility of DDGS and other high fiber ingredients.
Key findings:
1. In vitro activity of enzymes.
a. None of the 11 commercially available carbohydrase enzymes were effective for improving in vitro dry matter or gross energy disappearance in the simulated small intestine digestion or simulated large intestine fermentation when enzymes were added to corn DDGS.
b. Carbohydrase enzymes only increased in vitro dry matter and gross energy dissapearance in the simulated small intestine digestion without affecting the in vitro total tract digestibility of DM when applied to wheat middlings.
2. In vivo effect of enzymes. Feeding diets with high inclusion rates of high fiber ingredients (40% corn DDGS or 30% wheat middlings) decreased feed intake of 25-40 kg pigs.
a. Addition of carbohydrase enzymes increased feed intake and improved growth rate without changes in feed efficiency in pigs fed wheat middlings.
i. Effect of enzymes on feed intake may be the result of changes in gut physiological conditions.
1. Site of nutrient digestion. Similarly as observed in vitro, feeding wheat middlings and corn DDGS with carbohydrase enzymes increased the apparent ileal digestibility of DM, OM, GE, and CP, but it did not affect the apparent total tract digestibility of DM, GE, OM, or CP.
2. Characteristics of digestive content.
a. There were no differences in pH of gut contents of pigs fed diets containing enzymes vs. the control diets.
b. Adding corn DDGS and wheat midds increased the peak shear stress for stirring jejunum and ileum content. Addition of carbohydrase enzymes decreased this peak shear stress.
3. Immune response. Feeding wheat midds or corn DDGS to growing pigs excerts a different immune response in the small and large intestine. While pigs fed corn DDGS had greater expression of TNFα in colon, pigs fed wheat midds had greater expression of IL4 and IL25 in the ileum.
4. LC-MS metabolome. There were differences in metabolite composition of pigs fed wheat middlings and corn DDGS, and adding carbohydrases had no effect on the metabolome profile of pigs at any of the sections of the gastrointestinal tract.
Pedro E. Urriola, PhD
Department of Animal Science and Department of Veterinary Population Medicine
University of Minnesota