*Dr. William A. Dudley-Cash is a poultry and fish nutritionist and has his own consulting firm in Modesto, Cal. To expedite answers to questions concerning this column, please direct inquiries to Feedstuffs, Bottom Line of Nutrition, 5810 W. 78th St., Suite 200, Bloomington, Minn. 55439, or email [email protected]
AT the 2013 Arkansas Nutrition Conference, J. Lee of Texas A&M AgriLife Research and the Texas A&M System presented a paper titled "NSP Enzymes: Interaction with Each Other & Dietary Factors."
Non-starch polysaccharides (NSPs) are the portion of vegetable polysaccharides that are not starch. NSPs are the major components of dietary fiber in ingredients commonly used in poultry diets and are comprised of cellulose and non-cellulosic polysaccharides. The chemical definition of fiber is the sum of NSP and lignin.
Starch is a polysaccharide of alpha-linked glucose units that is easily hydrolyzed to glucose by endogenous amylase enzymes in the intestinal tract of monogastric animals, including poultry. Ingredients that contain large quantities of starch (corn, potatoes and rice) are easily digested by poultry.
On the other hand, Lee pointed out that monogastric animals lack the ability to hydrolyze the beta-linked polysaccharides that are present in NSPs. This distinction is important.
The growth of the ethanol industry has diverted more and more corn from the feed industry for use in fermentation to produce ethanol. Soybeans are a primary ingredient for the biodiesel industry. The result has been a dramatic increase in the cost of corn and soybean meal (a doubling or more) and proportional increase in the cost of poultry feed.
A major effort has involved identifying and evaluating alterative ingredients to substitute for corn and soybean meal in poultry feeds. Most alternative ingredients have associated higher levels of NSPs, including wheat, triticale, barley, rye, dried distillers grains with solubles (DDGS) and canola meal.
With the presence of NSPs, a reduction in the digestibility of multiple components of the diet is often seen, according to Lee. Replacing starch with NSP will have a negative influence on growth rate because less energy is available for absorption (Just, 1982 and 1984).
The addition of 4% NSPs resulted in a 10% reduction in the digestibility of starch, lipids and proteins for pigs. In particular, decreased digestibility of fatty acids and monosaccharides would occur due to increased intestinal viscosity. The increase in intestinal viscosity would lead to decreases in nutrient uptake, enzyme contact and net energy.
Even minor changes in intestinal viscosity have substantial impacts on nutrient digestibility and growth performance (Bedford, 1996). Numerous studies have reported growth depression when NSPs are included in poultry diets.
The viscous nature of soluble NSP results in physiological responses in the small intestine, including increased transit times, intestinal mass and turnover rates of mucosa cells, mucin and carbohydrate expression of goblet cell glycoconjugates and undigested constituents, which increase small intestine microbial activity, composition and size.
NSPs in the diet can change gut microflora. According to Lee, higher counts of anaerobic bacteria are observed in birds fed high levels of NSPs, which has been demonstrated to be a consequence of increased intestinal viscosity. Producers also may observe a change in consistency of the birds' excreta. Droppings will become wet and sticky, which may lead to reduced quality and potentially result in leg problems.
Poultry producers who want to improve performance and nutrient utilization, as well as expand their opportunities to include alternative feed ingredients in poultry rations, may want to then consider the dietary supplementation of exogenous enzymes.
In the last decade, the use of exogenous enzymes has expanded dramatically. Lee referenced reports (Adeola and Cowieson, 2011) stating that feed enzymes have saved the global feed market $3-5 billion per year, resulting in a global feed enzyme market of $650 million.
Although thousands of enzymes have been discovered, only a small number of enzymes are suitable for use in feeds. Exogenous enzymes must first survive the processing methods associated with the production of the diets. Exogenous enzymes also must be able to withstand the pH of the poultry gastrointestinal tract. Furthermore, substrate interaction time for these enzymes is limited due to the short rate of passage time in poultry. Last, the enzyme must prove to be effective.
Exogenous enzymes function to degrade the NSPs present in the diet by breaking the fiber chains in the cell walls into smaller fragments. By breaking down the cell wall of grains, carbohydrase inclusion has been shown to decrease intestinal viscosity and increase digestibility and performance.
Lee said the use of carbohydrases has been shown to be effective in high-fiber diets by decreasing intestinal viscosity and increasing feed efficiency in wheat-based diets. These enzymes have been shown to improve feed conversion ratio, nutrient and energy digestibility and result in advantageous alterations in gut microflora.
Xylanase is an enzyme that is often used either independently or in combination with other enzymes as part of an enzyme cocktail.
By degrading the backbone of xylans, such as arabinoxylan, xylanase breaks down carbohydrates into more digestible components. Additionally, xylanase may also improve phosphorus utilization by increasing cell wall permeability or liberating phytate that was previously bound, according to Lee.
Numerous studies have shown that birds fed diets supplemented with exogenous xylanase often exhibit improvements in growth performance and feed conversion.
Esmaeilipour et al. (2011) reported that xylanase inclusion reduced cumulative feed conversion by three to six points through days 15 and 23. They also observed an increase in retention of crude protein, dry matter and energy with xylanase inclusion. Improvements to the digestibility of fat, crude protein and starch have been documented as well.
According to Lee, xylanase inclusion has been able to overcome energy reductions in multiple trials. However, energy reduction is not necessary to observe improved growth performance. Improvements in feed conversion and average daily gain in wheat and wheat/barley-based diets, as well as corn/soybean meal-based diets, have been reported by a number of researchers.
Other studies involving xylanase indicate advantages in relation to gut health. It is suspected that xylanase supplementation starting at an early age results in the selective promotion of advantageous microflora.
Massey O'Neill et al. (2012) reported no improvement in performance from day 0 to day 21; however, at day 35, the improvement in feed conversion was significant. They suggested that the xylanase acted to help microflora development in the gut.
Lee noted that performance responses to xylanase inclusion are inconsistent, and most of this inconsistency appears to be related to diet composition.
When feeding xylanase in wheat or wheat/barley-based diets, improvements in feed conversion and average daily gain are frequent but not universal. Several studies using these NSP-rich diets have observed improvements, while other trials failed to produce differences. When using corn/soybean meal-based diets, both improvements to feed conversion and lack of improvement have been observed.
Since many of the grains used in poultry diets contain a variety of NSPs, the use of products containing a cocktail of enzymes ranging in specificity may be the most effective approach.
An enzyme complex aids in the digestion of multiple nutrients; an example of this would be an NSP-degrading enzyme cocktail, which is often used in combination with diets high in DDGS, wheat or barley. Enzymes included in NSPase cocktails can vary and may include xylanase, beta-glucanase and alpha-galacotosidase.
Despite a variance in effectiveness, the use of a cocktail of enzymes may prove more potent than when the enzymes are used separately.
Olukosi et al. (2007) reported an additive effect on growth performance with enzyme inclusion. They reported increased nitrogen digestibility with a cocktail consisting of xylanase, amylase and protease (XAP) alone and also when included with phytase. When compared in a reduced-calorie diet, the use of both XAP and XAP in combination with phytase improved the ileal digestibility of phosphorus.
Lee said there are conflicting reports in the literature on the ability of single and cocktail-type enzymes to positively influence growth performance. Having said that, Lee went on to cite a large number of research papers by various authors that reported positive responses to a variety of enzyme cocktails. The NSPase cocktails included xylanase, glucanase, cellulase, pectinase, mannanase, beta-glucanase, protease, amylase and phytase in an assortment of combinations.
Responses to the addition of NSP enzymes have been observed most frequently for weight gain and feed conversion, although improvements in apparent metabolizable energy and the digestibility of amino acids, crude protein, fat, starch, dry matter and phosphorus have been observed.
The speculation is that the NSP enzymes are effective in releasing bound nutrients from the NSP matrix. Significant improvements have been more consistently observed when the diets included ingredients that contained higher amounts of NSPs (wheat, barley, DDGS and canola meal).
This paper is wide-ranging in the scope of its consideration of NSPs and NSP enzymes. For those who are interested in searching for more detailed information, the paper contains 70 literature citations.
The complete proceedings of the conference may be found on the Arkansas Nutrition Conference website at www.thepoultryfederation.com/annual-events/nutrition-conference.
The Bottom Line
NSP enzymes produce positive responses in poultry, but perhaps not consistently. Consistency appears to be improving, which may be a reflection of new and better enzymes, or it may simply indicate that researchers are becoming smarter in designing their experiments.
There is still a long way to go in measuring the specific economic value of the nutrient responses so that nutritionists can utilize NSP enzymes in poultry diets more efficiently.