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Functional Additives
Monday, June 14, 2004 12:00:00 AM
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New Generation Phytase Makes Economic Sense

 
Dr Y J Ru

Regional Technical Services Manager, Danisco Animal Nutrition

 

 

A novel 6-phytase produced in yeast has been shown to be at least 20% more efficient than other phytases available on the market.  Because of this, it allows the feed manufacturer to further reduce the use of expensive inorganic phosphorus sources, with consequent additional improvements in production costs and reduced phosphorus pollution compared to other commercially available phytases.

 

The phosphorus contained in cereal grains and vegetable meals is only around 30% available to poultry. The rest is present bound as part of phytate and is unavailable and excreted by birds, because they lack the necessary enzymes (phytases) to liberate phosphorus from phytate.

 

Inorganic phosphorus is typically used as the main source of phosphorus in feed to satisfy the bird's phosphorus requirement.  However, this inorganic P is not completely digestible; for example, dicalcium phosphate (DCP) is typically only between 75 and 85% digestible. This means up to 25% of the phosphorus contained in the supplemental inorganic source may be excreted into the environment. This is not only economically wasteful; the release of phosphorus into the environment is associated with overgrowth of algae in watercourses (eutrophication), which leads to significant reductions in water quality and effects on aquatic life.

 

Finally the prohibition on the use of meat and bone meal, which is a cost-effective source of highly digestible phosphorus in the European Union, means that it cannot be used in feeds for poultry or pigs either within the EU or by producers supplying EU-destined poultry or pig products (e.g. Brazil, Thailand and China). Producers are forced to use more expensive inorganic phosphorus sources, increasing the cost of poultry production.

 

Phytase to the rescue

 

The obvious solution to the problems outlined above is to release as much as possible of the plant phosphorus bound by phytate.  The enzyme phytase, which breaks down the phytate molecule, is ideal. 

 

Phytases are produced by a number of micro-organisms, including yeasts and fungi.  While most are manufactured industrially in fungi, Phyzymeâ„¢ XP (Danisco Animal Nutrition) is a novel phytase produced in the yeast Schizosaccharomyces pombe.  It is known as a "6-phytase", meaning that it releases the phosphate group on position 6 of the myoinositol ring first, while 3-phytases attack the bond at the 3 position first. However, there is no evidence to suggest that the order in which the phosphate groups are removed affects the efficacy of the phytase.

 

Novel phytase out-performs competitor

 

One way to evaluate the efficacy of a phytase is to test it in diets which have been reduced in phosphorus and calcium beyond that which is typically recommended for phytase use.

 

In a study at Purdue University, USA, broilers were fed a negative control diet which was reduced in total phosphorus by 0.26% in the starter diet and 0.19% in the grower diet (0.115% reduction is typically recommended by phytase suppliers in commercial practice), and reduced in calcium by 0.37% in the starter diet and 0.31% in the grower diet (0.1% reduction typically recommended). The negative control diet did not contain phytase. Performance of broilers fed the negative control diet was compared to broilers fed the negative control diet supplemented with three levels of Phyzyme XP or compared to performance of broilers fed diets which had not been reduced in calcium and phosphorus (positive control). Feed intake, body weight, tibia ash and FCR were significantly worse in birds fed the negative control diet compared to birds fed the positive control diet (Table 1). The lowest level of phytase addition (500 FTU/kg feed) more or less restored bird performance to that of the positive control, suggesting that this phytase had an extremely powerful nutrient-releasing capacity.

 

Another way to evaluate a phytase is to compare its efficacy to other phytases. Data from broiler feeding studies show that there is a clear difference between Phyzyme XP and other phytases used in the feed industry. Performance data from 10 broiler trials conducted at research centres and universities across the world have shown that there is a clear difference between birds fed diets supplemented with different sources of phytase, in terms of body weight gain, feed intake and feed conversion over a 42-day growth period.

 

The trials measured and compared the efficacy of Phyzyme XP with a 3-phytase product in predominantly corn/soybean meal-based diets. All diets contained reduced levels of phosphorus and calcium to account for the release of these minerals by the phytase, which was included at different levels, ranging from zero (control) to 800 FTU/kg feed. A total of 89 treatment comparisons were made, 61 with Phyzyme XP and 28 with the 3-phytase. The relative bioefficacy between the two phytases was calculated for each of the three performance parameters (feed intake, body weight gain and feed conversion) by comparing the slopes of linear regression equations for the percentage response of the two products.

 

Over the whole growth period, the response to Phyzyme XP was greater than the response to the competitor for all three parameters. Figure 1 shows the relative improvement in body weight gain. At the recommended dose of 500 FTU/kg feed, Phyzyme XP was shown to be 1.44 times (44%) more effective than the competitor phytase. Similarly, feed intake was increased and feed conversion improved by Phyzyme XP 1.32 (32%) and 1.65 times (65%) more effectively than the competitor phytase, respectively. These values represent the average response from 0-42 days, which vary according to age. Never the less, at any stage of growth, Phyzyme XP was at least 20% more efficient than the 3-phytase in improving weight gain and feed intake.

 

Savings in practice

 

At the recommended dose of 0.01% Phyzyme XP, which delivers 500 phytase units per kg of feed, the total phosphorus level of the feed can be reduced by 0.138%, if DCP is used in the formulation. Furthermore, the superior action of this phytase on phytate also releases more calcium, allowing the feed's total calcium level to be reduced by 0.12%.

 

Assuming a DCP cost of US $0.25/kg, addition of 500 FTU/kg feed of Phyzyme XP, replaces 7.7kg DCP in the formulation and provides a gross cost saving of US $1.93/tonne of feed. When compared to the saving of US $1.60/tonne afforded by the same amount of 3-phytase activity, Phyzyme XP saves an extra US $0.33/tonne, if the cost of both phytase products is comparable (Table 2).

 

Although this represents a considerable feed cost saving, existing users of phytase in broiler diets can choose not to maximise the feed cost saving afforded by Phyzyme XP and instead opt to include a 20% lower phytase activity in the feed. In practice, this would mean using 400 FTU/kg feed (a dose of 80g/tonne) of Phyzyme XP to replace 500 FTU/kg feed (100g/tonne) competitor 3-phytase, or 750 FYT/kg feed (300g/tonne) competitor 6-phytase, to achieve the same performance as the competitor product, but at a 20% lower dose.

 

Superior environmental benefits

 

Table 2 shows that addition of Phyzyme XP at 500 FTU/kg feed can be used to replace 7.7kg of DCP in the formulation. When this is compared with the 6.4kg/tonne DCP spared by addition of a competitor phytase product, Phyzyme XP addition replaces 1.3kg/tonne (20%) more DCP. Remembering that DCP is not 100% digestible, replacing DCP with Phyzyme XP reduces phosphorus excretion, not only from phytate-bound P, but also from inorganic P sources. In one broiler study, Phyzyme XP reduced P excretion by 40% compared to a key competitor (Figure 2). Thus, adding Phyzyme XP to the feed formulation helps the producer to keep ahead of tightening environmental legislation, by reducing phosphorus emissions.

 

Why is it so effective?

 

Danisco Animal Nutrition's scientists have identified a number of possible reasons for the superior efficacy seen in poultry trials. For example, because all enzymes are proteins, they are at risk in the digestive tract from degradation by digestive proteases.  Phyzyme XP is more resistant to degradation by the endogenous protease pepsin than other phytase products (Figure 3). Secondly, it retains its high relative activity over a broader pH range (Figure 4). This means that it can remain active longer within the different parts of the digestive tract where pH levels vary.

 

Adding Phyzyme XP to broiler diets clearly has superior advantages, offering the feed manufacturer and poultry producer flexibility of cost savings whilst improving performance and reducing phosphorus waste.

 

Figure 1. Phyzyme XP improves broiler body weight gain more effectively than a 3-phytase

(0-42 days).

 

 

 

Figure 2. A novel 6-phytase improves the digestibility of phytate phosphorus in broilers.

 

 

 

Figure 3. Sensitivity of different phytases to pepsin at pH 2.

 


 

Figure 4. pH profile of relative activity of three phytases over a broad pH range.

 


 

Table 1. The effect of Phyzyme XP on performance and tibia ash of broilers at 42 days:

 

             ab Means within a column with a different superscript differ at P<0.05
             Corrected for different body weight (3 points in FCR for every 100g body weight)

 

 

Table 2. Extra feed cost saving due to addition of Phyzyme XP

 

                Excludes cost of phytase

 

 

For further information:

Danisco Animal Nutrition, Singapore

Tel: +65 6224 8600

Email: info.animalnutrition@danisco.com

          www.danisco.com/animalnutrition


 

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