Department of Poultry Science College of Agriculture and Life Sciences
North Carolina State University
Raleigh, NC, U.S.A.
Supplemental enzymes have become common additives to poultry and swine feeds as a means to improve nutrient utilization and production performance characteristics. Today, pentosanase (Non-starch Polysaccharide enzymes) are used in virtually all poultry and swine diets comprised of mainly of small grains, such as wheat, barley, or oats. In geographical areas where phosphorus emission is a concern, the use of phytase has become a standard feed additive in poultry and swine feeds. Enzyme blends are now available to improve the nutritional value of diets containing soybean meal, animal protein meals, or high fiber food byproducts. Most recently, enzymes are being considered as a means to control gut microflora and influence the enteric milieu of poultry and swine, especially in young animals most susceptible to enteric pathogen challenge. This presentation is a brief review of feed enzymes and their function and application to improve animal growth performance.
What are enzymes?
Enzymes are organic catalysts that can initiate or accelerate biochemical reactions, converting one or more organic substrate compounds into organic products that would not otherwise proceed at an appreciable rate (Schaible, 1970). Even the simplest living organisms contain multiple copies of nearly a thousand different enzymes. The first enzyme to be isolated was urease, crystallized by James B. Sumner in 1926 (Horton et al., 1996c). Most enzymes are named by adding the suffix "-ase" to the name of the substrate they act on or to a descriptive term for the reactions they catalyze. For example, urease has urea as a substrate; alcohol dehydrogenase catalyzes the removal of hydrogen from alcohols. However, a few enzymes, such as trypsin and chymotripsin, are known by their historic names (Horton et al., 1996c). Enzymes are categorized according to the general class of the organic reactions they catalyze. Oxidoreductases catalyze oxidation-reduction reactions. Transferases catalyze group-transfer reactions. Hydrolases, a special class of transferases that water serves as the acceptor of the group transferred, catalyze hydrolysis reactions. Lyases catalyze the lysis of a substrate, generating a double bond. Isomerases catalyze a structural change within one molecule. Ligases catalyze the ligation or joining of two substrates (Horton et al., 1996c). All digestive enzymes belong to the class of hydrolases. Today, isolated enzymes are used for a great variety of commercial purposes, including supplementation of enzymes to improve nutritional value of feed.
Enzymes are substrate specific
With the development of enzyme products targeting specific substrates, the use of enzymes to improve the nutritional value of feed has received increased attention. Since the 1920s, researchers have observed beneficial effects from enzyme supplementation in poultry feeds, particularly feeds that contain grains with a high fiber component (Hastings, 1946; Moran Jr. and McGinnis, 1968; Pettersson and Aman, 1989; Ritz et al., 1995).
Supplemental enzymes in the feed are used to achieve one or all the following objectives:
(a) Increase the animal's own supply (Schaible, 1970);
(b) Alleviate the adverse effects of antinutritional factors, such as arabinoxylans, β-glucans, etc; and
(c) Render certain nutrients more available for absorption and enhance the energy value of feed ingredients (Classen and Bedford, 1991; Lyons, 1993).
Several criteria must be met in order for an enzyme to be applicable in animal feeds. Adequate substrate (target substance) must be available in the feed for a specific enzyme being used; and the animal should be able to utilize the end product of enzyme action (e.g. fatty acid absorption from lipase supplementation), or benefit from the breakdown of specific substrates in the feed (e.g. fat digestion improvement from NSP breakdown by arabinoxylanase) (Dale, 2002). The enzyme should be stable during and after feed processing, stable in the feed until it is consumed by the bird, and stable in the animal's gut where it should have its greatest effect (Odetallah, 2000). Finally, the appropriate enzyme supplement should interact efficiently with its target substrate and be supplemented at levels sufficient for the amount of the target substrate. For example, xylanase should be used for wheat-based diets because it contains substantial amounts of xylan. In contrast, xylanase would be of little benefit in corn/soy diets because it contains a negligible amount of xylan.
Common enzymes used in animal feed
The major types enzymes used in animal feeds are categorized by their substrate specificity (Table 1). All enzyme preparations recommended for use to improve dietary nutrient utilization in animals are hydrolases (Modyanov and Zel'ner, 1983). Commercial enzymes products are typically a blend of several different enzymes that are effective on a wide variety of substrates that comprise feed. The enzymes with proven efficacies for animal husbandry include xylanase, arabinoxylanase, β-glucanase, cellulase, phytase (Choct and Kocher, 2000), proteases (Odetallah et al., 2003), and phospholipase (Santos et al., 2004b).
The following is a brief description of each of these enzymes, and their mode of action in poultry feed.
Non-starch polysaccharidases (NSP)
The use of enzymes active against NSP is now an established part of the feed industry and its effect on the nutrient utilization and performance characteristics of animals has been widely studied. The use of fungal and microbial enzymes to avoid the adverse effects of non-starch polysaccharides in cereal-based poultry diets has been studied for decades (Jensen et al., 1957), and interest in the effects of the enzymes and their modes of action has been sustained up to the present (Odetallah et al., 2002; Silva and Smithard, 2002). Chickens and turkeys do not produce enzymes that are capable of digesting xylans and β-glucans, which is why exogenous NSP-enzymes are added to the feed (Silversides and Bedford, 1999). The mechanism of action of the exogenous xylanases was long believed to be by the release of nutrients through the destruction of cell wall (Silversides and Bedford, 1999). Even though this idea is partially true, there is considerable evidence that enzymes elicit benefits other than simply releasing nutrients from cellular constituents (Silversides and Bedford, 1999).
Supplementing cereal-based diets with microbial enzyme preparations capable of hydrolyzing endosperm cell walls, may improve dietary nutrient availability by several means. Endoxylanase for example, degrades the xylan backbone of arabinoxylan into smaller units, which has several beneficial consequences. It renders the xylose units more available to monogastrics (Odetallah, 2000). It disrupts the water holding capacity of the NSP (Scott and Boldaji, 1997) and reduces the viscosity of the digesta in the small intestine (Bedford and Schulze, 1998; Choct et al., 1999a). Reduced digesta viscosity increases the diffusion rates of nutrients and endogenous enzymes, enabling the bird to digest and absorb more nutrients (Pawlik et al., 1990). Endoxylanase releases entrapped nutrients for the digestion by the endogenous enzymes of the bird (Chesson, 2000). Endoxylanase inhibits the proliferation of the fermentative microorganisms in the small intestine by increasing the digesta passage rate and nutrient digestion (Choct et al., 1999a). Thus, nutrient utilization is improved by reducing the competition between the host and its enteric microflora.
Many authors have observed improved nutrient utilization by dietary enzyme supplementation. Pettersson and Aman (1989) examined the effect of enzyme supplementation on the digestibility of nutrients in broilers fed wheat-based diets. Enzyme supplementation increased the digestibility of organic matter, crude protein and starch in the ileum, and increased the digestibility of organic matter and crude fat in the excreta. Silva and Smithard (2002) studied the effect of xylanase (Avizyme 1300, Finnfeeds International of Marlborough Ltd [EC Registration ATCC 2105]) on rye-based diets and observed that the reduction of small intestinal viscosity by the enzyme improved nutrient digestion and consequently performance. Several researchers have shown increased performance of broiler chickens fed cereal-based diets with enzyme addition (Jensen et al., 1957; Santos, 2003). Likewise, Ritz et al. (1995) observed improvement in body weight gain, and feed consumption of male turkeys fed xylanase supplementation.
Many authors have shown the interaction between pentosans, microflora, and enzyme supplementation. Fischer and Classen (2000) reported that bacterial count from the small intestine of broilers fed wheat-based diets was lower in xylanase-supplemented birds than the unsupplemented ones. Because dietary enzyme supplementation reduces the microbial population in the small intestine (Choct et al., 1995b; Dunn, 1996), the entire gut ecosystem changes. These conditions in the gut alter the composition and activity of intestinal microflora (Vukic-Vranjes and Wenk, 1996). Dietary enzyme supplementation changes the animal's gut microflora and decreases some of the adverse effects of microbial fermentation, such as the deconjugation of bile salts which reduces fat digestion (Langhout, 1999); reduced competition between the host and the microflora for nutrients (Bedford, 1995; Choct et al., 1996; Langhout et al., 2000); and atrophy of the intestinal villi and enlargement of digestive organs (Brenes et al., 1993a; Viveiros et al., 1994).
Although microflora fermentation in the small intestine decreases when xylanase is supplemented in the diet, microbial fermentation increases in the large intestine and ceca. Steenfeldt et al. (1998) observed that dietary xylanase supplementation decreased cecal content pH due to increased production of SCFA. They also observed a significant negative correlation between pH and the apparent digestibility of total-NSP (r= -0.73, P<0.0006). They also found a negative correlation between pH and apparent digestibility of xylose (r= -0.72, P<0.001) and arabinose residues (r= -0.69, P<0.001). Therefore, the results observed by Steenfeldt et al. (1998) indicate that degradation of cell wall arabinoxylan in the enzyme-supplemented diets increases the amount of material available for microbial fermentation in the caeca. This increased fermentation in the large intestine and caeca then leads to greater production of short-chain fatty acids that is utilized by the bird as energy, thus enhancing the benefits of the enzyme supplementation (Choct et al., 1996). Likewise, Choct et al. (1996) reported that volatile fatty acids (VFA) concentration in the caeca was not influenced by elevated amounts of soluble NSP, but it was significantly increased by enzyme supplementation. In contrast, they reported that ileal VFA was significantly higher in birds fed diets containing soluble NSP as compared to those fed the control (sorghum/soybean meal) or the enzyme-supplemented diets.
The response to dietary enzyme supplementation is dependent upon the age of the bird. Ward (1996) reported that dietary enzyme supplementation improved performance in older birds (22-42 days), but not in younger birds (1-21 days). Similarly, Odetallah et al. (2002) observed higher live weight of male turkeys fed enzyme supplementation at 84-112 days but not at 7-49 days as compared to the unsupplemented control birds. Older birds have a more mature gut ecosystem with a higher fermentation capacity than younger birds when diets contain a high amount of NSP. Therefore, the effect of the enzyme on the microflora, as a consequence of the NSP breakdown, is higher in older birds. Vukic-Vranjes and Wenk (1996) reported that the beneficial effect enzyme on the performance of broilers was completely eliminated by dietary antibiotic supplementation. This significant enzyme by antibiotic interaction demonstrates that the positive enzyme effect in older birds is, to a great extent, mediated by the activity of intestinal microbes.
In contrast to Ward (1996), Brenes et al. (1993a) observed improved performance of broilers fed enzyme supplementation, regardless of age (0-42 days). Mcknight (1997), however, observed a benefit of enzyme supplementation (Natugrain 33%, BASF) only when fed to young turkeys (up to 70 days of age). He attributed the diminishing effects of enzyme supplementation in his trial to gradual adaptation of turkeys to the wheat-based diets. Likewise, Leeson et al. (1996) reported that NSP enzyme supplementation to turkey diets had a positive effect on growth rate of turkeys up to 72 days of age but not subsequently.
Several other researches have studied the effects of enzyme supplementation on NSP-rich diets of poultry feed. Dietary enzyme supplementation has been shown to decrease gut viscosity and improve performance (Friesen et al., 1992; Preston et al., 2001), increase AME (Annison and Choct, 1991; Auclair and Larbier, 2000), and enhance the digestibility of dietary calcium and phosphorus (Jaroni et al., 1999), starch (Hetland and Svihus, 2001), nitrogen (Bedford, 1995; Huyghebaert, 2000), and fat (Friesen et al., 1992). Many of these studies have shown that AME was positively correlated to fat digestion (Friesen et al., 1992; Steenfeldt and Heindl, 2000). Smulikowska and Mieczkowska (2000) reported that 62% of the increase of the AMEn values was due to better fat digestibility when broilers are fed wheat-based diet supplemented with enzymes containing xylanase and β-glucanase activities. Hence, appropriate dietary enzyme supplementation can restore the digestion of starch, protein, and lipid, leading to more consistent and uniform growth performance (Choct et al., 1999a). Similar results have been observed with the supplementation of carbohydrases in diets containing legume and non-cereal grains (Bedford and Morgan, 1995; Annison et al., 1996). Furthermore, turkeys fed wheat-based diets supplemented with enzyme (Natugrain Blend and Lyxasan Forte, BASF - Germany) have been shown to have better feather scores than unsupplemented control birds because of a decrease in feather picking and aggression (Odetallah et al., 2002). Odetallah et al. (2002) suggested that this reduced aggressive behavior was due to improved amino acid availability and better intestinal comfort. Poor amino acid balance and perturbed gut microflora can stress turkeys (Ferket and Veldkamp, 1999). Moreover, Odetallah et al. (2002) reported that supplemental xylanase to turkeys decreased mortality rate. They stated that mortalities among the control-fed toms were primarily due to enteric infections, whereas mortalities among the enzyme treatment groups were due to cardio-pulmonary disorders often associated with the most rapidly growing birds.
There are some contrasting opinions on the effect of enzyme supplementation on feed intake. Some researchers have reported increases in feed intake after enzyme supplementation and attributed this effect to reduced intestinal viscosity and increased in passage rate (Bedford and Classen, 1992a; Antoniou et al., 1981). Other researchers reported a decrease in feed intake and attributed the enzymes effect on enhanced digestibility of carbohydrates, protein, and lipid (Annison, 1992; Scott, 2000). Still other researchers have observed no significant effect of dietary enzymes supplementation on feed intake (Ravindran et al., 1999a; McCracken and Quintin, 2000; Preston et al., 2001).
Enzyme has been shown to reduce the differences between different batches of wheat. Many authors have observed that the addition of NSP enzymes significantly reduces the variation among different wheat cultivars (Scott, 2000). Scott and Pierce (2001) measured the feeding value of western Canadian wheat by bioassays and reported that variation in AME among wheat or barley-based diets was significantly reduced with enzyme supplementation. Diets containing low AME cereal grains generally benefit more from enzyme supplementation than diets containing high AME cereal grains. Choct et al. (1995a) reported that enzyme supplementation significantly improved the nutritive value of a low-AME wheat diet (< 3,107 kcal AME/kg DM; Mollah et al., 1983; Rogel et al., 1987). Therefore, use of appropriate enzymes is an effective way of using grains with high NSP contents in poultry diets (Choct et al., 1999a).
The effect of enzyme supplementation on the performance and nutrient digestion has been reported to increase as the enzyme level increased. Odetallah (2000) reported that the level of dietary enzyme addition is crucial for improving the performance of turkey. Several researchers have shown dose-dependent responses for dietary supplementation of NSP-enzymes (Hesselman et al., 1982; Pettersson and Aman, 1989; Bedford and Classen, 1992a). Other workers, however, have not been able to demonstrate the increase in AME and performance by increasing the level of dietary enzyme supplementation (Annison, 1992). Furthermore, dietary supplementation of enzyme has been shown to alleviate the osmotic diarrhea and improve litter quality in poultry by reducing the amount of osmotically materials in the gut because it disrupted the water holding capacity of the NSP (Pettersson and Aman, 1988; Fischer and Classen, 2000).
Dietary enzyme supplementation occasionally has little influence on productive performance of poultry. Preston et al. (2000) studied the effect of xylanase supplementation on the performance and energy utilization of broilers fed diets containing 67% of wheat. They reported no significant effects of enzyme supplementation on performance and energy utilization. Odetallah (2000) attributed this poor enzyme efficacy to the low level of enzyme dosing (Odetallah, 2000). In agreement, Crouch et al. (1997) stated that one possible reason for the general lack of response with some enzymes might be due to an insufficient dosage of enzyme relative to the high NSP content in some cultivars of wheat. Other authors attributed poor enzyme efficacy to the inappropriateness of the enzyme for the type of grain (Friesen et al., 1992). Friesen et al. (1992) stated that an enzyme with xylanase or pentosanase activity is required for rye and wheat, and a β-glucanase or cellulase for oats and barley. Furthermore, a blended preparation of enzymes has been shown to be more effective on improving performance than single enzyme preparations (White et al., 1981; Santos et al., 2004b). When diets are supplemented with a blend of enzymes, the activity of one type of feed enzyme is facilitated by the activity of another (Ravindran et al., 1999b).
The effects of enzyme supplementation are dependant upon the source and type of wheat. Veldman and Vahl (1994) studied the effect of four wheat varieties supplemented with xylanase on the growth performance of broilers. The enzyme had a different effect on broiler performance for each variety of wheat. Saulnier et al. (1995) attribute these variations in enzyme effect among wheat cultivars due to their high heterogeneity in water-soluble arabinoxylan content. Wheat contains higher levels of pentosans when it is subjected to frost-damaged during seed maturation (immature wheat) than when it is grown under more ideal conditions (Ward, 1995). Santos et al. (2004a) reported that supplementation of a commercial enzyme blend that contain high level of xylanase and β-glucanase significantly reduced the adverse effect of high NSP content of frost damaged wheat when fed to turkeys.
Supplementations of β-mannanase in corn-SBM based diets fed to animals have been shown to improve performance parameters. β-D-mannanase or manna endo-1,4-β-mannosidase (Hemicell®) is an endohydrolyase enzyme that is a fermentation product of Bacillus lentus, and it degrades β-mannans. β-mannan is a polysaccharide with repeating units of mannose and galactose, and glucose are often attached to the β-mannan backbone. Hemicell® cleaves randomly within the 1,4-β-D-mannan chain of galactomannan, galactogluco-mannan, and mannan (McCleary, 1988). Odetallah et al. (2002) reported that β-mannanase Hemicell® supplementation on diets fed to turkeys from one day through the market age improved body weight gain and feed efficiency. These same results with β-mannanase Hemicell® have been seen in broilers (McNaughten et al., 1998) and finishing pigs (Chen et al., 1998). Jackson et al. (1999) suggested that the improvement in the animal performance is due to the effect of the enzyme on gut viscosity and consequently in gut digestion and microflora.
Phospholipase
Lipase is another enzyme that has been tested in wheat-based poultry diets because fat digestion is often compromised by NSP. Martin and Farrell (1998) studied the supplementation of lipase in wheat-based diets, while Al-Marzooqi and Lesson (1999, 2000) studied its effect in corn/soy diets. Both research groups hypothesized that supplemental lipase would improve the digestibility of fat when wheat or corn-based diets were fed to young birds because they exhibit a lower level of natural lipase production than older birds. In wheat-based diets, supplemental lipase was anticipated to be especially effective in increasing the digestibility of the fat that may be impeded by highly viscous water soluble NSP. However, dietary supplementation of lipase did not improve the performance of the chicken and ducklings, regardless of the type of cereal base diet. Al-Marzooqi and Lesson attributed the lack of lipase response to the contamination of the enzyme product with cholecystokinin by the microorganism responsible to produce the lipase. Cholecystokinin is a hormone that reduces feed intake.
Phospholipase (PLA2) is an experimental enzyme that has been studied in turkeys fed wheat-based diets (Santos Jr. et al., 2004b), but not in corn-SBM diets fed to broilers. Santos Jr. et al. (2004b) reported that PLA2 supplementation improved body weight gain and feed/gain of toms from 0-18 weeks. Also, they reported that dietary supplementation of PLA significantly increase AMEn compared to control toms from 9-12 weeks of age. Endogenous intestinal phospholipase A2 (PLA) catalyzes the hydrolysis of the ester bond at sn-2 position of glycerophospholipids (GPL), producing fatty acids and lysophospholipids (e.g. Lysophosphatidylcholine or Lyso-PC). The fatty acids are then absorbed from the lumen as part of the fat micelle. Lyso-PC, the predominant GPL product in the luminal content, is essential for the emulsification (lipid emulsification is the first stage of lipid digestibility) of water-insoluble lipids (Homan and Jain, 2001). Lyso-PC is a major amphiphile molecule, which acts to stabilize micro droplets of triglycerides, cholesterol, and other nonpolar dietary lipids that are otherwise insoluble in the aqueous environment of the intestinal contents (Carey et al., 1983). Also, PLA influences the capacity of the enterocyte to transport absorbed lipids into the circulation, which depends on cellular phosphatidylcholine synthesis controlled by the hydrolysis of phosphatidylcholine in the lumenal contents. Additionally, PLA posses an intrinsic secretin-releasing activity (Chang et al., 1999) that stimulates the release of pancreatic secretion and bicarbonate in the duodenum, which influences the digestion of others macronutrients. Thus, dietary supplementation of phospholipase may reduce the adverse effects of NSP by (a) facilitating the formation of micelles of triglyceride, cholesterol, and other nonpolar dietary lipids; (b) enhancing the capacity of the enterocytes to absorb lipids; and (c) increasing the digestion of the others macronutrients.
Phytase and cellulase
Phytase and cellulase are important enzymes used in commercial poultry practice. Phytate is an antinutrient present in all plant material that irreversibly chelates divalent cations and interferes with amino acid absorption in the gastrointestinal tract of birds as well as other monogastrics. Moreover, the fecal excretion of phytate phosphorus and chelated minerals is a major source of soil and water pollution when wastes are applied to farmland. Dietary phytase supplementation is used to improve utilization of phosphorus and other ionically active nutrients (i.e. amino acids, minerals), ultimately reducing mineral emissions (Odetallah, 2000). The action of cellulase is complex because cellulose is generally associated with other polymers, such as lignin and pentosans. Lignin encrustation renders access to cellulose by the enzyme difficult if not impossible (Sears and Walsh, 1993).
Proteases
Recently, protease on corn-SBM based diets has received considerable attention. Supplementation of poultry diets with enzyme mixtures that include proteases and amylases has produced significant improvements in growth performance (Greenwood et al., 2002; Burrows et al., 2002). Greenwood et al. (2002) reported that supplementing a corn-SBM broiler starter diet with an enzyme preparation containing a mixture of xylanase, protease, and amylase resulted in improvement in body weight at 14 and 42 days of age. Versazyme® is a serine-protease from Bacillus licheniformis PWD-1 (Williams et al., 1990; Lin et al., 1992) that contains a high amount of keratinase.
PWD-1 keratinase hydrolyzes a broad range of protein substrates, including casein, collagen, elastin and keratin, and displays a high proteolytic activity (Shih, 2001). Odetallah et al. (2003) studied broilers fed corn-SBM based diets at 18% crude protein (80% NRC 1994), 21% crude protein (93% NRC 1994), and 24% crude protein diet (100% NRC 1994) with 0.0%, 0.05% or 0.10% Versazyme® (PWD-1 keratinase) from 1-26 days of age. They reported that Versazyme® supplementation of corn-SBM based broiler starter diets improved chick body weight gains and feed conversion rates, and 0.10% Versazyme® (w/w) especially improved the growth performance of broiler chicks fed diets containing low or adequate amounts of protein.
Enzymes can modify gut microflora
Dietary enzyme supplementation may also serve to modify enteric microflora and promote growth as an alternative to antibiotic growth promoters. Antibiotics are effective modulators of enteric microflora and enteric health and they have been commonly used to promote growth in the poultry industry (Cook, 2002). However, due to the increasing public concern about the development of antibiotic-resistant pathogens, there is great interest in feasible non-pharmaceutical alternatives such as enzymes (McCracken et al., 2000). Lundeen (2002) stated that enzyme supplementation might be a tool available for modification of the microbial ecology of bird gut in the absence of antibiotics.
The gut is the natural habitat for a large and dynamic bacterial community, however some of these bacteria are potential pathogens. Studies of animals raised in germ-free conditions have provided important information about the effect of the gut's microflora on host physiology and pathology (Roberfroid et al., 1995; Falk et al., 1998).
The gut microflora contribute specific metabolic, trophic and protective functions. Through fermentation, the microflora use non-digestible dietary residues and endogenous secretions, and produce fermentation products of that benefit the host, such as short-chain fatty acids (SCFA) used as for energy and absorption of ions, and vitamin K.
The trophic functions of gut microflora include the control of epithelial cell proliferation and differentiation due to the production of SCFA, and development and homoeostasis of the immune system. The microflora provides the host some protection against pathogens as non-pathogenic bacteria occupy attachment sites to the brush border of intestinal epithelial cells, thus competitively excluding colonization of pathogenic bacteria, competing for nutrients, and secrete compounds that inhibit the growth of unfavorable bacteria.
The microbial milieu of the gut is species-specific and varies depending on animal age, physiological state, gut site, and diet composition. The presence and nature of dietary fiber, the main bacterial substrate, especially has a significant influence on the characteristics of the gut microflora. Langhout (1999) observed that dietary NSP significantly increases gut populations of pathogenic bacteria at the expense of beneficial bacteria. In addition, colonization of enteric pathogens is dependent upon the degree of resistance afforded by the stability of the resident microflora and the integrity of the intestinal mucin barrier in the animal (Ferket, 2003). Older animals are much less susceptible to the colonization of enteric pathogens than young animals because they have a more stable and diverse gut microflora that competitively exclude pathogen colonization. In the poultry business Salmonella is a pathogenic bacteria of concern.
Salmonella is a Gram-negative, non-sporulating, aerobic, and opportunistic bacterium that can cause enteric lesions in poultry, and it is a major risk factor for human food safety. Disturbance of the microflora during salmonellosis (mainly due Salmonella enterica, serovars Enteritidis and Typhimurium) causes significant economic losses in the poultry industry, and can cause alimentary toxicosis and severe infections in people who consume contaminated poultry meat or eggs. Because Salmonella are commonly found in the gastrointestinal tract of poultry without causing clinical symptoms, contamination of meat may occur unnoticed during slaughter and meat processing.
Although hygiene and vaccination may reduce the risk of Salmonella in poultry, nutritional factors can modulate the degree of Salmonella colonization in poultry (Hafez, 1999). Enzyme supplementation has been shown to decrease Salmonella colonization (Moran et al., 2003).
References are available on request
From Proceedings of the "Midwest Poultry Federation Convention", St. Paul, Minnesota, U.S.A.
