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Scientifi cally Speaking …


By Matthew Wedzerai


Matthew Wedzerai holds an MSc in Animal Science (Specialisation: Animal nutrition) from Wageningen University, The Netherlands. He also holds a Diploma in Pig husbandry & Animal Feed, PTC+ College, The Netherlands. He has 7 years’ experience in the pig husbandry and animal feed industry and has been a writer of articles based on scientific research since 2014.


WHY COMBINING PHYTASE AND NSP- DEGRADING ENZYMES IS NOT ALWAYS HELPFUL?


Research has proved that a combination of phytase and NSP- degrading enzymes has a better effect on nutrient digestibility and utilisation, compared to supplementation by individual feed enzymes. Synergistic effects of these combinations have been reported in several studies. But, oftentimes, these enzyme combinations bring variations in results, and do not always give their full potential. It’s valuable to have an insight into the causes of these variations, and possible ways of optimising the use of a combination of phytase and NSP-degrading enzymes (carbohydrases).


This article will mainly address the causes of sub-optimal performance in poultry diets, of combined phytase and NSP-degrading enzymes. Xylanase is one of the main NSP-degrading enzyme that will be used to highlight the effects of combining phytase with NSP-degrading enzyme on poultry performance.


Why phytase and NSP-degrading enzymes? In poultry diets, phosphorus is one of the most expensive component of poultry diets after energy and amino acids. Feedstuffs of plant origin contain anti-nutritional factors such as phytic acid and non- starch polysaccharides (NSP); these limit phosphorus utilization in poultry, and also, bind and reduce the utilisation of other nutrients. Supplementation of phytase and NSP-degrading enzymes has been shown to improve P digestibility, increase the digestibility of protein and other minerals, and improve apparent metabolizable energy values, in poultry diets. Negative effects of phytic acid The use of phytase is aimed at countering the negative effects of phytic acid. The following are the main negative effects of phytic acid: It binds approximately two-thirds of P in most feedstuffs of plant


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origin, resulting in poor P-digestion. It reduces the utilisation of nutrients other than P by binding


to them. Thus, the presence of phytic acid in poultry diets can result in reduced efficiency of nutrient utilization and hence increased cost of feeding, and environmental pollution. - Due to its negative charges at acidic, neutral and basic pH conditions, phytic acid can complex cations at all pH conditions in the gastro-intestinal tract, thereby reducing the bioavailability of these cations. It can interact with protein directly to form electrostatic bonds,


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thereby reducing the availability of protein for digestion in the pro-ventriculus and ventriculus of poultry. - Energy digestibility can be reduced when phytic acid binds carbohydrates and lipids.


Negative effects of non-starch polysaccharides (NSPs) Non-starch polysaccharides are indigestible by poultry, and they can reduce the availability of nutrients within the cells by encapsulation (Bedford, 2000; Bedford and Schuzle 1998). In addition, NSPs such as soluble β-glucans and arabinoxylans can increase digesta viscosity, which, in turn, can reduce nutrient absorption and digestibility. Several research studies have shown a reduction in feed


conversion and fat digestion of broilers due to an increase in dietary concentration of soluble arabinoxylans.


Synergism of phytase and NSP-degrading enzymes Phytase and NSP-degrading enzymes can hydrolyse phytic acid and NSPs, respectively, alleviating the negative effects of these anti-nutritional factors. In poultry, for example, supplementation of phytase and xylanase in combination has been shown to improve ileal digestibility of amino acids and weight gain. Synergism in improving nutrient utilization occurs since NSP-


degrading enzymes can hydrolyse the NSP in cell walls, thereby increasing the accessibility of phytase to phytic acid. Overall, synergism of phytase and NSP-degrading enzymes on


nutrient utilization and performance can occur if:  The supplemental NSP-degrading enzymes are able to hydrolyse NSP in the diet,


 NSPs are limiting the accessibility of phytase to phytic acid,  The phytic acid made available by NSP-degrading enzymes is hydrolysed by phytase, and,  Nutrients made available by the actions of phytase are limiting performance.


Thus, the response to supplementation of a combination of these


enzymes is variable and dependent on several factors, including the type of phytases used, endogenous phytase activity, dietary NSP composition, dietary digestible phosphorus concentration and dietary concentration of multivalent cations. Now, let’s assess how these factors affect synergism or the potential effects of supplemental phytase and NSP-degrading


PAGE 16 MAY/JUNE 2018 FEED COMPOUNDER


Comment section is sponsored by Compound Feed Engineering Ltd www.cfegroup.com


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