Feed Enzymes – Their Benefit

The use of feed or exogenous enzymes in poultry diets has found
widespread commercial acceptance as a strategy to improve nutrient
utilization, performance and uniformity, and reduce feed cost and
nutrient excretion.

The use of feed or exogenous enzymes in poultry diets has found widespread commercial acceptance as a strategy to improve nutrient utilization, performance and uniformity, and reduce feed cost and nutrient excretion. Additionally, the reductions in pathogenic microflora and the improvements in health and welfare of birds are sometimes quoted as direct results of feed enzyme use.^{1, 2}

The response to feed enzymes in terms of feed cost reduction and/or performance improvement depends on parameters such as feed ingredient and enzyme costs, dietary specifications, bird age and ingredient quality. Advertisement

Research focusing on the bird’s endogenous enzyme system has dealt mainly with limitations of endogenous enzyme production due to the bird’s age but also due to the presence of antinutrients such as fibre and phytate.³ Young birds are more limited in the types and amounts of enzymes necessary to utilize a high carbohydrate and vegetable protein diet, thus affecting nutrient digestibility and the overall performance.⁴

Furthermore, endogenous losses, including secretion of enzymes, are also reported to be influenced by feeding antinutrients such as phytate (inositol phosphate or IP6) and fibre.^{5, 6} Other factors affecting endogenous enzymes have also been studied, including inhibitors of endogenous enzyme activities (e.g., amylase inhibitors), which can cause an increase in the production of endogenous amylase resulting in reduced performance.⁷
 
There is some direct evidence that the supplementation of exogenous enzymes can also positively influence endogenous nutrient losses, including a more efficient production of endogenous enzymes).⁷ These types of research studies provide further support of the high value of enzymes in today’s poultry industry. Furthermore, they give greater credibility to nutrient matrix values, which are typically applied with feed enzymes today as a result of both direct feed nutrient digestibility improvement and more efficacious use of endogenous compounds, specifically endogenous enzymes.

Benefits of feed enzymes
The effect of exogenous enzymes on performance (e.g., feed conversion – FCR) improvements has been well documented over at least the last 20 years of their widespread commercial use. Such evidence includes studies focusing on non-starch polysaccharide-hydrolyzing enzymes (NSPases) such as xylanases and beta-glucanases widely used in wheat- and barley-based diets or phytase, amylase, and protease enzymes used in various types of poultry diets.^{8, 9, 10} More recently, research focusing on phytase and its combination with fibre-hydrolyzing enzymes as well as phytase combination with amylases and proteases, further supports the high value of feed enzymes to poultry producers today.^{11, 12}

The response to feed enzymes in terms of feed cost reduction and/or performance improvement will depend on a number of parameters, including feed ingredient and enzyme costs, dietary specifications, bird age, and ingredient quality, to name a few. As an example of performance improvement response with enzymes, Cowieson summarized peer-reviewed published studies with broilers fed corn-based diets with various exogenous enzyme activities (xylanases, amylases, proteases, mannanases, galactosidases and pectinases) reporting that FCR was improved over control diets (without addition of any enzyme) by 0.88% to 10.5%.13 Such improvements are certainly relevant to the poultry industry, especially if they can be replicated in commercial practice. In addition, the variability in FCR response suggests the importance in evaluating availability and levels of substrates for enzymes in feeds and matching them with specific types and levels of enzyme activities to achieve the optimal response.

Today, most poultry diets contain feed phytase enzymes, so evaluating the effect of other enzyme activities together with phytase on poultry performance and economics seems to be more practical. There is also an ongoing discussion as to whether the combined enzyme application (phytase with other enzyme activities) delivers an additive, sub-additive or synergistic effect on nutrient utilization and performance.14 It is likely that the answer depends on a variety of factors, including the type of diets and enzyme activity combinations used. For example, Rosen,15 in his research review, found that average FCR improvement in 17 published studies was 5.09% in diets supplemented with phytase and xylanase combined compared to 2.66% and 2.28% when supplementing xylanase or phytase alone, respectively.16 This suggests a somewhat synergistic effect for these enzyme activities. Similarly, Cowieson and Adeola saw a 10.4% improvement in FCR of broilers fed a corn-based diet with the addition of phytase, amylase, protease and xylanase.17 However, they saw ‘only’ a 7.3% and 8.4% FCR improvement when using phytase only or a mixture of amylase, protease and xylanase only, respectively, resulting in a sub-additive effect of combining all the enzyme activities.

In most commercial diets today, feed enzymes are included with their own nutrient matrix values. These matrix values are largely based on research related to observed feed nutrient and energy digestibility improvements due to hydrolyses of polysaccharides that encapsulate protein, starch; a direct release of nutrients such as phosphorus from phytate; and the effect on digestibility of starch and protein.^{_{18, 19, 20}} In addition, there is a body of evidence suggesting that feed enzymes may also spare endogenous compounds. This action can occur through digestive enzymes hydrolyzing enzyme inhibitors or lectins found in feed; direct supplementation of endogenous enzymes missing in gastrointestinal tract (GIT) of poultry (fibre hydrolyzing enzymes); supplementation of enzymes present at low levels (e.g., phytase); or supplementation of enzymes, which are significantly reduced in young birds.21 More recently, information on the effect of phytate and phytase on endogenous losses further support that the feed enzyme effect not only has a strong benefit on direct feed nutrient digestibility and energy present in feeds, but also on the more efficient use of endogenous proteins, energy, and other compounds.^{22, 23}

Importance of endogenous enzymes
Amylase, isomaltase, maltase, chymotrypsin, pepsin, trypsin and lipase are examples of enzyme activities typically discussed as produced by poultry at significant levels. Furthermore, gastrointestinal mircoflora, specifically in the lower GIT, contributes to the digestive enzyme pool through production of enzyme activities such as phytase and fiber hydrolyzing enzymes.²⁴

Amylase secretion by salivary glands of poultry has been found to be very limited.²⁵ Similarly, the amylase activity in the crop is very low as is also the case in the glandular stomach and gizzard.²⁶ On the other hand, levels of amylase progressively increase from the duodenum, jejunum to ileum due to a secretion by the pancreas, intestinal secretions, and a small presence of amylase in bile.²⁷ Pancreatic amylase production in chicken is regulated by neural factors instead of gut hormones.²⁸ Thus, variability in a-amylase production is likely related to differences in dietary stimulus levels, such as presence or absence of starch in the GIT of poultry. Indeed, it has been reported that feeding a low starch diet resulted in reduction of pancreatic amylase production.²⁹ Liu et al. found that not only did phytate significantly decrease the concentrations of amylase in the jejunum, but also the concentrations of sucrase, Na+K+-ATPase, and glucose by 10 to 22%, clearly showing the negative effect of phytate as an antinutrient on endogenous carbohydrase activity and metabolism of carbohydrates.³⁰ Furthermore, Yuste et al. reported that digestibility of starch in a variety of ingredients is lower in 21-day-old broilers than in adult roosters, which indicates that the GIT of young broilers is not fully developed to digest starch.³¹ This was supported by Noy and Sklan, who saw lower amylase activity in young chicks compared to older birds. Similarly in turkeys, Persia et al. observed that starch disappearance in Meckle’s region was 79% and 86% for 6- and 12-week-old birds, respectively, further supporting the age-dependent endogenous enzyme production/activity.^32,33 Furthermore, amylase inhibitors found in most cereals and legume grains can have a substantial negative impact on digestion of starch).³⁴

The proventriculus or glandular stomach secretes both acid and pepsinogen, activating it into pepsin in an acid environment. Pepsin is also present in the contents of the muscular stomach, where most of the peptic digestion occurs.³⁵ As with amylase, it is suggested that pepsin concentration is affected by the amount of substrate (e.g., protein levels) present in feed and there is evidence that carnivorous birds produce more pepsin compared to grain-eating birds.³⁶ Additionally, feeding diets with high levels of phytate, fibre and less digestible protein has shown to result in increased pepsin production in pigs and more recently in poultry. Cowieson and Ravindran suggested that the amino acid composition of pepsin compared well with types of endogenous amino acid losses associated with feeding high levels of phytate.^{37, 38} Other proteases produced by the pancreas are chymotrypsin and trypsin. An example of how other antinutrients may potentially affect endogenous enzyme production can be seen in the work of Boguslawska-Tryk, who noted that Cobb broilers that were fed diets with increased cellulose levels had significantly higher pancreatic protein content as well as elevated proteolytic enzyme activity (including trypsin and chymotrypsin). Noy and Sklan found a 15% increase in crude protein digestibility in four-week-old broilers compared to very young (one week) birds, showing also that protease activity, like amylase, is influenced by age in young birds.^{39, 40}

The main source of lipase production is the pancreas. Bile, produced by the liver, is involved in activation of pancreatic lipase. Lipase has also been found in gastric contents, probably due to a result of a duodenal reflux.⁴¹ It seems that fat digestibility is greatly influenced not only by the type of fats/oils used in poultry feeds but also by the presence of antinutrients such as soluble non-starch polysaccharides, which are responsible for the increase in digesta viscosity.⁴² The authors saw 10% and 40% improvement in FCR of young broilers when feeding diets containing either soy oil or tallow, respectively, in high versus low jejunal viscosity causing feeds. Nitsan et al. reported that lipase activity is significantly limited in young poultry.⁴³ This was supported more recently by Gracia et al. who compared the total collection ether extract digestibility for broilers at different ages.⁴⁴ The authors found that digestibility was 76.1% and 85.2% in 7- and 28-day-old broilers, respectively. Furthermore, emulsification of fats and activation of lipase by bile salts can be affected by excessive deconjugation of bile salts due to a high presence of gut microflora.⁴⁵ Thus controlling microbial proliferation in the GIT through various means, including feed enzymes addition, should make a contribution to improvements in fat and energy digestibility.⁴⁶

Other enzyme activities such as maltase and isomaltase are present in brush borders of intestinal tissue and are responsible for single sugar production before their transport across the intestinal membrane. Liu et al. reported a significant effect of phytate on reduction of sucrase and Na+K+-ATPase in chicks suggesting that presence of antinutrients in feed can also negatively influence these endogenous enzymes.⁴⁷

Poultry either lacks or contains only minor levels of other specific enzyme activities – phytase and fibre-hydrolyzing enzymes – necessary to deal with substrates present in today’s poultry diets.⁴⁸ While intestinal microflora is capable of some level of phytate P dephosphorylation and fibre fermentation, these processes typically occur in the lower part of the GIT (e.g., cecum) to have a major impact on antinutritive properties of these compounds and/or contribute to a significant amount of nutrients available for poultry.⁴⁹

Relationship between endogenous and feed enzymes
Commercially, there are two major feed enzyme groups, amylases and proteases, which are also produced at significant levels by poultry. Sometimes lipases are mainly present as part of multiactivity feed enzyme products, which makes it difficult to directly evaluate the effect of this individual activity on endogenous enzymes. Other feed enzyme activities – fibre-hydrolyzing enzymes (NSPases) and phytase – are not directly produced by the bird; however, their presence in the GIT of poultry via feed supplementation has a large impact on feed nutrient digestibility improvements and also directly affects efficient use of endogenous compounds, including enzymes.

Amylases and proteases
Gracia et al. saw a reduction in the relative weight of the pancreas in broilers fed a-amylase supplemented feed. Jiang et al. reported that feeding increasing levels of feed amylase resulted in a negative quadratic response on anterior intestinal content of amylase and protease.^{50, 51} Although both protease and amylase were increased with an increase in amylase supplementation, the highest amylase dose reduced both enzymes’ presence. In terms of bird performance, the authors showed that the highest dose of amylase used increased daily gain and feed intake by 4.5% and 3.6%, respectively. This result would suggest that performance response was not only related to the effect of amylase on nutrient digestibility improvement but also influenced by reduction in endogenous losses through reduction in endogenous protease and amylase production. Mahagna et al. also reported that intestinal content of protease was reduced with supplementation of amylase and protease.⁵² These findings agree with Ritz et al., further supporting complementary action of exogenous and endogenous enzymes.⁵³ Ritz et al. also observed an increase in jejunal and ileal sections villus length when supplementing three-week-old turkey diets with a-amylase, suggesting that products (e.g., dextrin) resulting from an increase in starch digestibility positively influenced other enzymes such as maltase.⁵⁴

In the study of Jiang et al., which was already mentioned, the authors saw a tendency (P=0.05) in reduction of pancreatic amylase with increased levels of feed amylase potentially indicating a negative feed-back mechanism.⁵⁵ This was supported to some degree by a reduction in amylase mRNA expression suggesting the supplemented amylase effect on pancreatic amylase is on a transcriptional level. Since pancreatic amylase production in chicken is likely regulated by neural factors instead of gut hormones, the increase in a-amylase production is related to a more dietary stimulus. According to Brannon, transcription of pancreatic a-amylase increases in response to presence of dietary starch in rats, further supporting the hypothesis that if exogenous amylase is able to improve starch digestibility early on, there is an opportunity for reduction of endogenous a-amylase production.^{56, 57}

Isaksen reported that incubating wheat or corn starch with pancreatic amylase and increased levels of phytic acid resulted in reduced activity of amylase and the degradation of starch was almost halved at the highest tested concentration of phytic acid.58 The author also found that the negative effect of phytic acid on starch degradation was counteracted by increasing levels of Ca++ or by adding feed phytase enzyme. Ca is required in activation of amylase and potential chelation of Ca by phytate reduced the activity of amylase.

It is possible that some observed variability response in studies with amylase supplementation is due to the origin of amylase, amylase activity, cereal type and feeding mash versus pelleted feeds.⁵⁹ In his study, Cowieson et al. saw 7% FCR improvement in corn/soy-based poultry diets pelleted at 70°C containing a mixture of amylase, protease and xylanase.⁶⁰ However, there was no effect on FCR in the same diets pelleted at 85°C. The authors hypothesized that the performance improvement at 70°C was related to improvements in starch digestibility; however, pelleting at 85°C potentially improved retention of energy from starch (gelatinization) not giving enough space for amylase to further improve dietary energy and performance.

Huo et al. showed that microbial protease enzymes could inactivate trypsin inhibitors and lectin in raw soybean meal and low temperature extruded soybeans.⁶¹ It seems that bacterial proteases were more effective in breaking down the trypsin inhibitors than the fungal protease used in this study.

More recently, Brenes et al. showed that an inclusion of 25% high oleic acid sunflower seeds resulted in low weight gain, fat digestibility, amylase and lipase activity compared to a control diet without any sunflower seeds.⁶² The addition of enzymes containing lipase, phospholipase and their combination to a diet high in sunflower seeds improved fat digestibility and bird performance. In addition, the enzymes were able to offset the negative effect of sunflower seeds on relative pancreas and liver weights as well as endogenous amylase and lipase activities.⁶³

Finally, Cowieson and Ravindran mentioned in their work that trypsin contains relatively high concentrations of alanine, glycine and serine while pepsin is particularly rich in leucine, glycine and aspartic acid.⁶⁴ Some researchers noted the effect of feed enzymes on amino acid digestibility and its correlation to amino acids present in endogenous protein.⁶⁵ More specifically, Remus et al. showed the effect of a feed enzyme mixture based on amylase, protease and xylanase on amino acid digestibility improvements in poultry.⁶⁶ The authors reported that the improvements were greatest for Val, Thr, Arg, Ile, Cys and Leu. Given the association of these amino acids with endogenous amino acids, it seems that the effect of feed enzymes was particularly dependent on influencing endogenous amino acid values potentially including endogenous enzymes.

Fibre-hydrolyzing enzymes and phytase
Bedford suggested that high digesta viscosity caused by soluble non-starch polysaccharides present in ingredients such as wheat or barley affects not only gut-enterocytes turnover rates, level of microflora and coccidial populations but also endogenous-enzymes synthesis rate.⁶⁷ Svihus et al. saw a reduction in intestinal viscosity, caused by soluble beta-glucans, the gizzard, and small intestine weight in barley-based diets supplemented with beta-glucanase enzyme compared to unsupplemented diets.⁶⁸ Additionally, the authors noticed that the pancreas weight as a percentage of body weight tended to decline with enzyme addition. This would suggest that the presence of fiber and its negative effect on nutrient digestibility also directly influences pancreatic enzymes overproduction. Brenes et al. saw also a reduction in soluble beta-glucans, gizzard weight and jejunum length in birds fed barley-based diets supplemented with fibre-hydrolyzing enzyme, however, the authors did not see such responses in birds fed wheat-based diets suggesting that the level of antinutrients (e.g., soluble NSPs) is important in order to impact endogenous losses.⁶⁹ Furthermore, Cowieson et al.  reported that intestinal viscosity due to the presence of soluble NSPs was increased by temperature processing of feeds likely due to its contribution to changes in the level of soluble NSPs.⁷⁰ Xylanase addition reduced viscosity and improved performance.

Cowieson et al. reported that phytic acid irritates the GIT and causes an increase in excretion of endogenous amino acids, minerals and sialic acid.⁷¹ Furthermore, Cowieson and Ravindran found that ingestion of phytate P at 2.4 g and 4.0 g per kg of broiler diet resulted in a 47% and 87% increase in endogenous amino acids and N flow compared to a diet without phytate P.⁷² The addition of feed phytase reduced the endogenous amino acid flow. The authors further noted that phytic acid not only increases amino acid flow but also changes the composition of the endogenous protein. Their data tend to suggest that an increase in the secretion of endogenous enzymes, particularly pepsin, is possible with an increase in ingestion of phytic acid. More recently, Liu et al. found in 2008 that feeding broiler diets containing high phytate concentrations depressed body weight and FCR, whereas phytase supplementation improved the performance.⁷³ They also found that in the duodenum, phytate decreased the activities of disaccharidases, Na+K+-ATPase, and glucose concentrations by 5 to 11%, but phytase enhanced the concentrations of amylase, sucrase, maltase, Na+K+-ATPase, and glucose by 5 to 30%. In the jejunum, phytate decreased the concentrations of amylase, sucrase, Na+K+-ATPase, and glucose by 10 to 22%, and phytase alleviated the negative effect of phytate on these variables. Diets containing increased phytate upregulated the mRNA expression of the sodium glucose cotransporter gene in duodenum but not in the jejunum.

The information above offers some evidence of the effect of feed enzymes on endogenous enzymes production through variety of mode of action. It is apparent that research into this area will continue and potentially further support a positive role of feed enzymes in poultry feeds.

Summary
Feed enzymes provide significant benefits to the poultry industry today and are used with great flexibility in a variety of diets and markets. Feed enzymes are typically valued for their effect on feed cost reduction, performance and uniformity improvement, reduction in nutrient excretion and contribution to the well-being of birds.

References available at www.canadianpoultrymag.com.