Despite all the technical developments in animal production, ways of getting the most out of feedstuffs are still being investigated. Non-starch polysaccharides (NSPs), which make up 7-19% of the plant-based raw materials in broiler diets, are tricky customers. Finding the right combination of enzyme activities to unlock nutrients from a variety of raw materials is essential. To be able to do this scientists need to understand the complex structures of NSPs.
Arabinoxylan chains, the predominant NSP, are one of the most important anti-nutritional factors found in plant feedstuffs. Breaking down these chains increases both digestible nutrient content and energy. When the nutrients released by exogenous enzymes are taken into account and thus the improved digestibility that this provides, the nutrient density of broiler diets – and hence cost – can be reduced. New research has demonstrated the feedase effect in broilers fed a low nutrient density diet. Despite a 3% nutrient dilution, due to the action of the feedase the metabolisable energy and digestible amino acid content was similar to that of a standard wheat and soya diet.
The mechanism by which NSPs lock-up nutrients making them unavailable to the birds, is complex. By encapsulating nutrients or increasing the viscosity of the digesta, soluble and insoluble NSPs inhibit the digestion of starch, amino acids and lipids. These encapsulating properties depend on the quantity and properties of the NSP, however, there are important differences between the NSPs found in the raw materials. For example, the arabinoxylan structures of corn and wheat NSPs differ, which has a direct impact on the efficacy of enzymatic degradation. The more NSPs in a diet, the more digestibility is affected.
There is still much to learn about the impact of indigestible components in many feed ingredients. Understanding the complex nature of the NSP content boosts the potential to improve the digestibility of feed. Not all carbohydrases act in the same way on the NSP components because they are a variable substrate. This is why greater effects are seen by adding a combination of carbohydrases to the diet.
Their specificity requires that different enzymes are used to degrade each component of the indigestible dietary fraction. The ability of efficient multi-enzyme solutions to improve global feed digestibility is known as the feedase effect. By breaking down the indigestible fractions of feed and and associated anti-nutritional factors, more nutrients are released. So the mode of action is a synergy between the effects of arabinofuranosidases (Abf) and xylanases – along with beta-glucanases and cellulases (Figure 1).
Abf, as Feruloyl esterase, are debranching enzymes which, in combination with xylanases, are very effective in breaking down highly-branched arabinoxylans. Abf enzymes remove the arabinose residues from the xylose chain. The xylanases then have better access to the xylose backbone for hydrolysis. This synergistic action results in a greater breakdown of arabinoxylan – reducing its anti-nutritional effects. Therefore releasing more nutrients, such as amino acids and lipids. This improves the overall efficacy of feed energy utilisation. An extra quantity of metabolisable energy can then be measured. The feedase effect is therefore also a matter of understanding the combined effect of different enzymes on the same feed, thereby enabling it to release nutrients more efficiently.
The efficacy of the feedase effect has already been demonstrated in scientific studies and commercial evaluations. Nutritionists have found that they get better nutritional efficiency by adding an efficacious enzyme complex to a variety of diets. Several studies measured the performance of broilers fed a series of reformulated diets. The addition of a feedase recovered the reduction in FCR seen in the reformulated diets. Demonstrating that more nutrients were released from the diet by breaking down the indigestible fraction. By raising performance to the level of the positive control, a feedase offers feed cost savings.
A new study looked at the effect of adding a feedase (Rovabio Advance, Adisseo) to standard or diluted broiler diets in terms of nutrient digestibility and energy utilisation. The trial was carried out at Adisseo’s Center of Expertise in Research and Nutrition (CERN) in France. Broilers were fed 1 of 4 dietary treatments between days 12 and 22 – after being fed the same starter formulation (days 1 to 11). The commercial control was compared with this same feed diluted by 3% (using 3% sand) and the diluted feed including the feedase. The digestibility of dry matter, amino acids and gross energy were determined by analysis of feed, excreta and digesta.
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Feed intake was not affected by the sand dilution of the diets and faecal energy digestibility was similar in the unsupplemented diets. However, the apparent metabolisable energy (AME) content was significantly lower in the diluted diet compared with the control. This effect was associated with changes in total nutrient content. The addition of the feedase significantly improved energy uptake. This led to an increase in the AME content of the diluted and standard diets by 2.8% and 2.9% respectively (Table 1). As a consequence, the AME content of the diluted diet plus feedase was similar to that of the standard unsupplemented diet. This demonstrated that the feedase effect fully compensated for the 3% nutrient dilution.
At ileal level, amino acid digestibility was around 75% for all treatments. Amino acid digestibility significantly increased by an average of 4.4%, when the feedase was added to the diets. Again showing that nutrient availability was restored in the diluted diet by the feedase effect. The authors of the published study highlighted the importance of considering the entire nutrient matrix when adding enzymes to broiler diets.
Carbohydrases are added to broiler diets to improve feed efficiency with the aim of increasing the metabolisable energy. However, energy is not a nutrient as such. It is the amount of energy produced by nutrient combustion. These nutrients include valuable protein. In a world demanding more protein that is both cheaper and more sustainable – feedase could be part of the solution.
New research has shown that using a feedase enables broilers to maximise energy utilisation and amino acid digestion from reformulated diets. By adding a feedase to the diluted ration broilers were able to obtain the same level of AME and amino acids as from the unsupplemented control diet. These lower nutrient density diets require less costly raw materials and can include more by-products, hence resulting in feed cost savings.
Ensuring optimum degradation of NSPs potentiates the effects of endogenous enzymes. By considering the overall effect of enzymes on the indigestible dietary fraction, the aim of the feedase is to maintain poultry performance and improve gut function, while reducing diet costs. Nutritionists can now formulate diets to meet the needs of broilers, producers and customers alike. The sociological, environmental and economic impact of feeding broilers a lower nutrient density diet is beyond doubt.
Maamer Jlali, Pierre Cozannet, Marcio Ceccantini and Sofia Zenagui
References available on request.