Enzymes are active proteins that accelerate the breakdown of specific feed components to release nutrients for digestion and absorption. Enzymes are typically used in swine diets to degrade feed components resistant to endogenous enzymes, inactivate antinutritional factors, and supplement endogenous enzymes that are not present in sufficient amounts (Thacker, 2013). Enzymes typically have designations with the suffix “ase” and are commonly produced by bacteria, fungi, or yeast. The most commonly used enzymes in swine diets are phytase, carbohydrases, and proteases (Jacela et al., 2009b). Phytase is certainly the most widely used among the enzymes due to its efficacy in releasing phosphorus from phytate. Phytase is reviewed in a single topic (Phytase in Swine Diets), while carbohydrases and proteases are detailed here.
Carbohydrases are enzymes that degrade carbohydrates, which include starch and non-starch polysaccharides. Non-starch polysaccharides are components of the cell walls of plant ingredients that are not degradable by the pig, including cellulose, hemicellulose, pectins, α-galactosides, β-glucans, and xylans. Carbohydrases most commonly used in swine diets are β-glucanase and xylanase, but α-amilase, cellulase, pectinase, α-galactosidase, β-mannanase, and others are also commercially available (Thacker, 2013). The use of carbohydrases could provide potential benefits particularly in diets formulated with the addition of ingredients with greater concentration of non-starch polysaccharides, such as barley, wheat, and grain co-products like distillers dried grains with solubles (Jacela et al., 2010c; Jones et al., 2010). Carbohydrases could improve the nutritional value or allow greater inclusion rate of these ingredients in the diet.
Proteases are enzymes that degrade proteins and act on protein-based anti-nutritional factors. Proteases used in swine diets have the ability to degrade a wide range of proteins, including less digestible proteins, such as glycinin and β-conglycinin in soybean meal-based diets (Chen et al., 2017). Proteases are often added to the diet in combination with carbohydrases, but single proteases are also commercially available (Zuo et al., 2015). The use of proteases could provide potential benefits particularly in the nursery, as pigs experience a decrease in enzymatic activity at weaning. Moreover, proteases could aid in the digestion of soybean proteins that are less digestible by weanling pigs and in the degradation of soybean allergens, particularly glycinin and β-conglycinin (Zuo et al., 2015).
Carbohydrases and proteases have often been shown to improve digestibility of nutrients and availability of energy of feed ingredients (Kiari et al., 2007; Emiola et al., 2009; Zuo et al., 2015). Recently, xylanase has been associated with a potential reduction in finisher mortality (Zier-Rush et al., 2016). However, the ability of in-feed enzymes to improve performance has not been proven consistent (Jacela et al., 2009b; Jacela et al., 2010c; Jones et al., 2010; Torres-Pitarch et al., 2017). The inconsistent effects of in-feed enzymes on performance could be due to denaturation of enzymes in the stomach, prompting the use of enzymes that are active over a broad pH range and are resistant to the action of gastric enzymes (Thacker, 2013). Moreover, the type and level of enzymes in a commercial product should match the type and level of substrates present in the feed ingredients included in the diet to achieve a better response to in-feed enzymes. For example, diets based on wheat probably would respond more to added xylanase, while barley would respond more to β-glucanase (Jacela et al., 2009b). Ultimately, the inclusion of enzymes in swine diets needs to be economically justified.