Skyrocketing feed costs has producers and nutritionists taking a closer look at enzymes to improve digestion and absorption of dietary components.
There has been a tremendous increase in interest and use of various types of dietary enzymes in swine diets to improve nutrient digestibility.
Enzymes are biologically active proteins that break specific chemical bonds to release nutrients for further digestion and absorption.
Proteases are enzymes that break down proteins. Lipases are enzymes that break down fats, and carbohydrases break down carbohydrates.
All of these enzymes can improve nutrient digestion and increase energy absorption. The most widely used enzyme in U.S. swine diets has been phytase, an enzyme that improves phosphorus digestibility in a wide variety of plant-based feed ingredients, such as corn and soybean meal.
The chemical characteristics of plant-based feed ingredients are very diverse (Table 1 ). The effectiveness of commercial enzymes and enzyme mixtures depends primarily on how well they are matched to the specific chemical characteristics of the ingredients used in swine diets.
For example, the amount of non-starch polysaccharides, which are complex carbohydrates that make up fiber in feeds, are relatively indigestible in pigs. Their range in digestibility is from 10% to 37%.
In pigs, fiber can be defined as a nutritional fraction in an ingredient that is resistant to digestion by the enzymes in their gastrointestinal tract. By this definition, cellulose, hemicellulose, lignin, pectins and β-glucans are the major components of fiber.
Cellulose is a complex carbohydrate made up of glucose linked by β-1,4 glycosidic bonds, which cannot be broken by the digestive enzymes in the small intestine of the pig.
Hemicellulose, found in high concentrations in the cell walls of plants, is associated with cellulose and pectin and consists of several non-starch, non-cellulosic polysaccharides including arabinoxylans, glucomannans and galactans.
Fiber has been considered an anti-nutritional factor for young pigs because it can decrease nutrient digestion, especially protein, amino acids and minerals. It can also increase the rate of stomach emptying, which further reduces nutrient absorption.
Biofuel By-Products Set the Challenge
The increased use of corn for fuel ethanol production and the increased use of fats and oils for biodiesel production are contributing to increased amounts of low-energy, high-fiber by-products for animal feeds. Pigs can only moderately utilize fiber for energy, unlike cattle, which can utilize fiber extremely well to meet their energy needs.
In order to improve the energy value of fiber in swine diets, effective commercial enzyme products need to match the carbohydrate composition of corn, soybean meal and distiller's dried grains with solubles (DDGS), as shown in Table 2 .
Compared to corn and soybean meal, DDGS contains a significant amount of fiber, which may play a significant role in decreasing dry matter (DM) digestibility of the diet. The main components of fiber in the DDGS are cellulose and insoluble arabinoxylans, similar to fiber in corn. Substituting 25% DDGS for corn and soybean meal in a young pig diet will increase the dietary fiber from 14% to 19%.
What the Research Shows
The addition of dietary enzymes to swine diets in efforts to improve nutrient digestibility has been researched for decades.
However, the majority of commercial enzyme products have been targeted toward young pigs or poultry — both with limited hind-gut fermentation capacity — and have typically been added to diets containing barley, oats, peas, rye or wheat. Only a few studies have evaluated their use in corn-soybean meal diets.
The most common fiber-degrading enzymes that have been supplemented in pig and poultry diets are β-glucanase, xylanase and cellulase. In general, fiber-degrading enzymes may have several modes of action, including:
Partial hydrolysis of soluble and insoluble fiber;
Decrease in digesta viscosity to improve lower gut microbial fermentation and energy value;
Rupturing of fiber-containing cell walls, thereby making the contents available for digestion; and
Enzymes in Basic Diets
Causing shifts in the population and activities of intestinal microflora.
Several studies have shown that when wheat and hull-less, barley-based diets are fed to young pigs (less than 55 lb. in body weight), responses to non-starch polysaccharide degrading enzymes are positive and relatively consistent, where digestibility of protein and energy and pig performance are all improved.
For growing-finishing pigs (more than 55 lb. in body weight), research results have shown a declining response to enzyme supplementation in wheat or barley-based diets as pigs get older. Data from several studies range from no response to dietary enzyme supplementation to clear, significant improvement in nutrient digestibility and/or growth performance.
However, a significant and positive effect on protein digestibility and numerical improvements in energy has been observed after dietary enzymes have been added in some trials, even when there was no growth performance response.
For corn-based diets, relatively few studies have been conducted to determine the effects of adding dietary enzymes on nutrient digestibility.
Results from one study showed no significant effect on protein and energy digestibility when adding β-glucanase to simple corn-soybean meal diets for weaned pigs.
Enzyme Potential Greatest In High-Fiber Diets
Similar results were seen in another study where adding multiple enzymes (cellulase, hemicellulase, xylanase, amylase, α-galactosidase) to diets for growing pigs (more than 95 lb. body weight).
When corn-soybean meal-based diets contained 20% wheat or wheat middlings/bran, however, significant benefits to xylanase supplementation on growth rate and/or feed conversion in growing/finishing pigs have been observed.
More recently, researchers at JBS United in Sheridan, IN, reported that adding an enzyme preparation to diets containing 30% DDGS increased growth performance in nursery pigs. Whether dietary enzyme additions will enhance growth performance in grow-finish diets containing increased levels of corn fiber is not known.
Research is underway to evaluate the effectiveness of various commercial enzyme products on improving the energy value of high-fiber, corn-based by-products for swine.
In general, the use of exogenous enzymes to degrade indigestible dietary fiber has yielded inconsistent results. Possible reasons for these inconsistent responses include:
Different grains and grain by-products have different dietary fiber (substrate for the enzyme) composition and content. For instance, wheat and rye are rich in arabinoxyloses, whereas barley is rich in β-glucan. Corn has much lower fiber content than barley and wheat and, as a result, the response to supplemental enzymes is small in simple corn-soybean meal diets.
However, if corn-soybean meal diets are supplemented with high-fiber by-products that contain significant quantities of insoluble cell wall material, the potential for a response to an effective enzyme source (particularly xylanse) is increased considerably.
Potential responses to enzymes will be greater in younger pigs because daily energy and amino acid intake often limits the ability of the pig to achieve its lean gain potential.
In addition, poor nutrient utilization has been partially attributed to the immaturity of the digestive system, including the breakdown of fiber.
Overall, the potential response to enzyme supplementation is greatest when feeding poor-quality (high fiber) ingredients to young pigs.
Contributions to this article were made by Guowu Xu, Midwest Ag Enterprises, Marshall, MN; and Brian Kerr, USDA-ARS, Ames, IA.