Choosing enzyme solution depends on many factors

Choosing enzyme solution depends on many factors

Supplementation of enzymes that are deficient early in a bird's life may help improve feed digestion and utilization.

*N.E. Ward is with DSM Nutritional Products in Parsippany, N.J.

THE poultry industry continues to face daunting challenges that stretch from live production to a global economy that leaves little to chance.

Over a span of decades, small but persistent innovations have kept the poultry industry competitive, and often at the envy of other livestock production enterprises.

Yet, for an industry that thrives on small efficiencies, one of the greatest ironies is the energy that goes unexploited in some of the best feed ingredients. Indeed, poultry retrieve only 70-75% of the energy from a corn/soybean meal diet because 85% and 50% of the gross energy in corn and soybean meal, respectively, is recovered (National Research Council, 1994).

Adding to the irony, feed comprises nearly 70% of the cost of production, and the energy component in the diet is the primary driver of cost. At today's ingredient prices, 10 kcal/lb. of feed represents $2.00-3.00 per ton of feed ($4.50-6.60/kg).


Nutritional dilemma

Upon hatch, the young bird must quickly switch from a lipid-dense yolk sac to a diet high in carbohydrates. The disappearance of the yolk sac might explain the temporary decline in digestibility at days 5-9, when the chick transitions to a contemporary diet (Thomas et al., 2008). Of course, the intestinal system eventually cooperates, but hastening the 14- to 21-day maturation process would favor energetics.

Furthermore, ingredients contain roughly 10-15% or more non-starch polysaccharides (NSPs) that interfere with nutrient digestibility. This indigestible fiber in corn, soybean meal and other ingredients shields nutrients from digestive processes, largely accounting for the aforementioned unrecovered energy. As we learn more, we find that various factors mitigate starch digestibility.

Nutritionists are tasked with matching nutrient requirements with a rapidly transforming physiology. In a short time, not only do changes in NSP level and composition occur, but protein digestibility is age and ingredient dependent (Rynsburger, 2009). One approach is an enzyme strategy that simultaneously addresses the dynamics of physiology, NSP and other substrates.


Digestive development

A juvenile bird's intestinal tract is problematic because digestive and absorptive functions are inadequate. Pre-starter diets attempt to tackle this shortcoming by providing highly digestible nutrients (Noy and Uni, 2010). Among other consequences, poor early nutrition can lower myofiber nuclei and cause irreversible reductions in muscle cell size and, ultimately, breast yield (Mozdziak et al., 2002).

During the days following hatch, the immature pancreas limits the luminal presence of critical enzymes such as amylase, trypsin, chymotrypsin and lipase. Over the ensuing days, pancreatic amylase secretion trends higher until 19 days, followed by trypsin and then lipase (Sklan and Noy, 2003; Figure 1). Little difference occurs in this regard between chicks and poults (Noy and Sklan, 1995).

Some uncertainty exists on whether enzyme activity or absorptive capacity limits chick growth. Generally, enzyme secretion in fast-growth chicks is not commensurate with the nearly twice the feed intake as leghorn chicks (Ravindran, 2003). Although an expanded intestinal surface area may compensate for low enzyme output, increased intestinal enzyme activity is proposed to improve feed utilization (Iji et al., 2001).

Digestibility studies. The physiological maturation of the intestinal tract is attained two to three weeks post-hatch, although breeder age, feed type and other factors can tweak this process (Thompson and Applegate, 2006; Maiorka et al., 2004; Swatson et al., 2002).

In University of Illinois studies, chicks obtained only 85% as much metabolizable energy (ME) from a simple corn/soybean meal diet at three to four days of age, as opposed to 21 days (3,000-3,377 kcal/kg; Batal and Parsons, 2003). Others concurred (Jimenez-Moreno et al., 2009; Olukosi et al., 2007; Batal and Parsons, 2002; Sell, 1996; Noy and Sklan, 1995), indicating that intestinal maturation stretches into the grower period. During this time, young birds struggle to procure nutrients from a high-quality diet.

Thomas et al. (2008) identified age- and cereal-related differences in ME and digestibility of starch and fat. Broiler chicks 7-10 days of age withstood considerably less nutrient uptake than older chicks.

Poults, likewise, exhibited marked improvements in fat uptake from days 5 to 19 — clear evidence of a maturation process (Sklan and Noy, 2003).

Young chicks are particularly sensitive to protein digestibility, in part because of large amino acid demands for muscle and organ development. From four to 21 days of age, digestion of nitrogen increased from 78% to 92% (Noy and Sklan, 1995). For corn, the protein and amino acid digestibility was 15% lower at five days of age than at 21 days (Adedokum et al., 2007). Certainly, limited endogenous protease secretions early in life cripple digestibility at a time of intense demands.

Across different ingredients, apparent ileal amino acid digestibility in broilers was elevated at 28 and 42 days of age, as opposed to 14 days (Huang et al., 2005). For corn, crude protein digestibility was higher at 42 days compared to 14 and 28 days. Methionine, lysine and threonine digestibilities were also lowest (P < 0.05) at 14 days.

An overwhelming number of studies confirm inefficient digestion following hatch. Age-dependent nutrient uptake closely tracks pancreatic and endogenous enzyme secretions; thus, villi development and bile secretion are vital. However, once the physiological changeover is complete, the ability to recoup energy from ingredients remains hampered by the presence of NSPs.


NSP content

About 90% of plant cell walls are composed of NSPs that sequester proteins, starches and lipids. The fibrous barriers besiege the starchy endosperm and aleurone, interfere with nutrient digestibility and hinder phytate dephosphorylation (Slominski, 2011). The physicochemical complexity can disrupt digestive dynamics because insoluble NSPs can imbibe water and shorten digesta residence (Choct, 2006).

NSPs are not digestible by intestinal enzymes. Grinding, conditioning and pelleting and chewing or gizzard action partially ruptures these walls, but the accessibility of the cellular constituents remains limited. It is hardly surprising that younger birds are especially prone to the negative aspects of NSPs (Boros et al., 1998; Petersen et al., 1999; Marquardt et al., 1996).

Cellulose, hemicellulose and pectins are the three major NSPs in feed. Cellulose is a structural polymer of repeating glucose units and is the most globally abundant fiber. Cellulases are essential enzymes for degradation.

Hemicellulose (pentosans) includes lower-molecular weight components that vary in water solubility. Arabinoxylans, beta-glucans and mannans fall within this classification. Enzymes that degrade hemicelluloses are generally called xylanases, pentosonases or hemicellulases, none of which are secreted in the intestinal tract.

Last, the pectins or pectic polysaccharides are high in galacturonic acid and prone to viscosity. Pectins cement cells together, and their depolymerization exposes other polysaccharides to the same fate. While virtually absent in cereals (Table 1), pectins and oligosaccharides predominate in soybeans and canola (Bach Knudsen, 2013). Studies espouse the benefits of pectinases — a reference to a wide range of pectin-degrading enzymes — in combination with other enzymes (Marsman et al., 1997; Malathi and Devegowda, 2001; Kocher et al., 2002; Vahjen et al., 2005). The success of galactosidase has been variable (Pettersson and Pontoppidan, 2013).

Certainly, the composition of NSPs varies widely due to genotype, geographical location and climatic conditions (Choct, 1997). Even so, arabinoxylans, beta-glucans and cellulose prevail in cereal grains, while pectins and oligosaccharides reside mainly in leguminous proteins.


NSP branching

NSP complexity is enhanced with attached residues and branching that markedly influence physiochemical properties (Collins et al., 2012). For example, arabinoxylan is composed of a xylose backbone with arabinose components. Acetyl, coumaryl, feruloyl and diferuloyl groups can crosslink to form clusters that sterically impede access to the xylan backbone by xylanase, thus thwarting degradation (Appeldoorn et al., 2010).

Corn arabinoxylan is nearly 100% substituted such that pure xylanase is rendered virtually ineffective (Agger and Meyer, 2012; Appeldoorn et al., 2010; Saulnier et al., 1995; Gruppen et al., 1993). That wheat arabinoxylans are less branched might explain — at least partially — the effectiveness of xylanase in wheat-based diets, whereas with corn, xylanase alone is seldom of consequence.

In addition, heavy branching of 1,4-beta-arabinogalactan in soybean meal restricts access to cleavage sites (Vahjen et al., 2005; Pettersson and Pontoppidan, 2013). For pectic substances, heavy methylation further aggravates the degradation process.


Dietary NSP

Table 2 is a compilation of the primary NSPs in a broiler feeding program. In this example, an all-vegetable commercial diet was used with 3% dried distillers grains plus solubles (DDGS). Going from the starter to the finisher, soybean meal declines while corn increases with subsequent changes in type and total NSPs.

A 22% increase in arabinoxylan (and starch) coincides with the higher corn level in the finisher diet. Oligosaccharides and pectic polysaccharides decrease 20-30% with reductions in soybean meal. Logically, one enzyme or the same combination of carbohydrases would not deliver the same benefit across an entire feeding program.



Starch is the primary energy source for poultry. Starch digestion is not necessarily quick and efficient, and granule structure, cultivar, heat and moisture can affect digestibility (Tester et al., 2003; Stevnebo et al., 2006). Starch granules may be encased by a rigid protein complex or NSP-based cell walls that interfere with amylase-starch action (Svihus et al., 2005; Classen, 1996) and help explain the inverse relationship between NSPs and starch digestion (Bach-Knudsen, 2013).

Poultry are prone to "starch overloading," and the kinetics of feed intake come into play (Carre, 2004; Svihus, 2001). An emphasis on high feed intake — probably exacerbated by pelleting — can lower starch digestibility, as does vitreousness (Correa et al., 2002). Drying corn by artificial means can foster the presence of resistant starch (Bhuiyan et al., 2012).

Starch digestibility improved 3-8%, while fat digestibility increased 9-15% from day 7 to 14 in poults (Fasina et al., 2004). Batal and Parsons (2002) reported similar findings, while in another study, alpha-amylase (endo-acting) improved seven-day gains and feed:gain, which ultimately affected 42-day weights (Gracia et al., 2003).


Critical enzymes

Feed enzymes can improve animal performance and/or lower feed costs. These include carbohydrases, proteases, phytases and others (Table 3).

Enzymatic dismantling of NSPs exposes internalized proteins, lipids and starches to endogenous enzymes (Le et al., 2013). Primary targets are cellulose, arabinoxylans and mixed linked glucans from cereals and pectic polysaccharides and oligosaccharides from plant protein sources. Thus, multiple carbohydrases need consideration.

Amylase is an important enzyme not only when pancreatic secretions are limited but later in high-corn feeds. Xylanase and protease can expose starch and augment digestion. Proteases are gaining in prominence and can be quite responsive in starter diets (Ward and de Beer, 2012), although low-quality ingredients, trypsin inhibitors and marginally deficient dietary protein benefit from feed proteases (Angel and Ward, 2010; Pontopiddan et al., 2012).

Phytase terminology now includes flex-dosing and super-dosing to portray the phytase-derived performance enhancement that goes beyond phosphorus nutrition. New and improved phytases more completely dephosphorylate phytic acid. This can elevate blood myoinositol (Figure 2; Aureli et al., 2013), a simple carbohydrate that participates in glucose production. Other factors probably contribute to the performance-boosting effect of feeding three to five times normal phytase levels (Cowieson et al., 2013).

In corn-based diets, debranching or ancillary enzymes can remove covalently bound branches on arabinoxylan to provide greater access by xylanase (Vries and Visser, 2001). Attention to these enzymes by the feed industry has been scant yet is a main focus in those industries where complete transformation of biomass is essential (Agger and Meyer, 2012).


Enzyme synergisms

Part of the success of an enzyme composite resides with potential synergies. Increased availability of commercial enzymes broadens opportunities to understand this collaboration, some of which have been discussed (Adeola and Cowieson, 2011; Slominski, 2011; Cowieson, 2010; Woyengo et al., 2010; Ward, 2008).

On the other hand, some expectations of theoretical synergisms or additivities have gone unmet, the result of factors yet to be resolved.


In the end

The rapidly developing intestinal system requires 14-21 days to become fully operational, a period that could constitute 55-60% of the life span of the broiler. Supplementation of enzymes that are deficient early in life represents a possible solution, while others target key substrates in any given feed. Enzymes must be chosen with scrutiny and will be the focus on an upcoming article.



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1. Relative NSPs (%) in feed ingredients











































Soybean meal







Canola meal













Wheat DDGS








2. Relative changes in NSP by in broiler feed stages







Total NSP






















Finisher, % of starter








3. Enzymes important to poultry feed ingredients of plant origin

Common name





To degrade linear beta-1,4-xylan; cereals



beta- and alpha-glucanases degrade glucans to glucose


Pectic polysaccharides

Heterogenous group of enzymes based on cleavage site of the substrate; protein sources



Breaks alpha-1,6-galactosidic bonds; soybean meal, canola meal



Degradation of cellulose to subunits



Degradation of mannans found in soybean meal

Debranching enzymes

Various side chains

Cleaves sidechains from main chain NSP in corn, soybean meal and others



Across all plant ingredients



For protein digestibility, particularly in young birds



For all starch-based ingredients, primarily corn

Choosing enzyme solution depends on many factors



Volume:86 Issue:04

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