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Phytase use in poultry diets: Going beyond phosphorus release

Phytase was developed to reduce the diffuse phosphorus pollution from intensive agriculture. First commercialised in 1991, phytase is now present in over 60% of monogastric feed, and possibly even in a higher percentage of poultry diets, in a growing market that exceeds $300 million US dollars per year. The savings to be made with the use of phytase can easily be three to four times this amount.

By Tiago Tedeschi dos Santos, Rob ten Doeschate and Hadden Graham, AB Vista Feed Ingredients, UK
Since first commercial utilisation, phytase has mainly been considered to be a tool to increase phosphourus (P) availability/digestibility from vegetable sources and so reduce the inclusion of higher cost P sources. Here, phytase releases the P bound in the phytate molecule, increasing the availability/digestibility of this mineral to the animal. Thus, increasing the inclusion rate of phytase would be expected to release additional P from the indigestible feed phytate and consequently allow an even greater substitution of higher cost P sources.
When phytases act on the phytate molecule, they also increase the solubility of the phytate while reducing its anti-nutritional effect. Phytate is known to be an anti-nutrient, affecting an increase in mucus production and the loss of amino acids, altering patterns of sodium secretion into the gut and influencing the absorption of minerals. Part of the anti-nutritional effect of phytate is related to its link with minerals at pH values higher than 4.0, reducing the availability of those minerals to absorb in the small intestine.
Increasing intact protein
Also, the link between phytate and proteins reduces protein digestibility. This results in increased amounts of intact protein in the small intestine, to which the animal reacts by increasing hydrochloric acid (HCl) and pepsin production. In the presence of phytate in the diet an increase in pancreatic juice and mucus production has been shown, which can be reduced back to normal levels by phytase addition. The increased mucus production may be a direct effect from the phytate (an irritant effect) or an indirect effect in response to the increased pepsin and HCl production.
All this translates into an increased endogenous flow of amino acids and minerals to the gut and reduced sodium (Na) re-absorption. As the main anti-nutritional effect of phytate occurs when the molecule has six or five bound P units, the release of P is not necessarily correlated with the reduction of the anti-nutritional effects of phytate. Three different phytases included at the same activity had different abilities to bind to (kM) and release P from phytates with six, five or four bond P units. The phytase with higher affinity (lower kM) to phytate with six or five bound P units had a higher ability to reduce the anti-nutritional effects of the phytate, even when releasing the same amount of P (Figure 1).
Higher enzyme doses
To use a phytase focusing on the reduction of the anti-nutritional effect of phytate, it is necessary to go beyond the release of P obtained by the enzyme. Initially a higher dose of phytase would have been considered to give an equivalent decrease in the need for supplemental inorganic P in the diet, looking for a further reduction in the cost of the diet while maintaining animal performance. However, an alternative approach is to look to eliminate the anti-nutritional effect of the phytate through higher enzyme doses, thereby increasing nutrient absorption and animal performance. One study provided high doses of phytase (12,500 FTU/kg) for broilers in a diet with a reasonable available P level (0.25%), and observed improved performance. A second study observed not only higher performance but also higher content of hepatic carotenoids in poultry fed with higher doses of phytase.
Several trials with higher doses of phytase using diets with normal levels of P have already shown better poultry performance, but this increase of performance was always correlated to an increase in P digestibility even if the diet did not have lower levels of P. Interestingly, in all these trials the increase in performance with higher doses of phytase was correlated to an improvement in the feed conversion ratio.
Turkeys and broilers
Two further trials evaluating the inclusion of high doses of phytase (Quantum from AB Vista) in broiler and turkey diets are described below. In the 84-day turkey trial the negative control (NC) was formulated with -0.13% Av P, -0.143% Ca and -0.03% Na compared with the positive control (PC), and Quantum was included at 250, 500, 1000 and 2000 FTU/kg in the NC. The PC diets met breed standards for Ca and Av P levels.
In this trial, 500 FTU/kg Quantum recovered performance in male and female birds compared with the PC, while higher doses of phytase (1000 - 2000 FTU/kg) improved average weight gain and numerically reduced feed conversion (Table 1). In the broiler trial, the NC was again formulated with -0.13% Av. P; -0.143% Ca and -0.03% Na compared with the PC and Quantum phytase was added at 500 and 1250 FTU/kg. In this trial (Table 2), 500 FTU/kg Quantum phytase recovered animal performance to the level found with the PC, and 1250 FTU/kg gave better feed conversions compared with PC at 21 days and no difference in body weight gain but numerically better feed conversion at 35 days.
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Correct enzyme
The concept of using phytase at high doses to reduce the anti-nutritional effect of phytate means that there is an opportunity to redefine nutritional knowledge. Animal requirements to date have been determined in the presence of phytate and thus the anti-nutritional effects driven by its presence. When using a high dose of phytase to reduce or eliminate the anti-nutritional effects of phytate, special attention needs to be paid to the choice of the correct enzyme. Ideally this product needs to be active at low pH and have higher affinity with IP6 and IP5, the phytate molecules with higher anti nutritional effects.
The overall diet formulation also needs to be considered as the absence of phytate will change other nutrient requirements. Commercially it is suggested to include an enhanced E. coli phytase at 500 FTU/kg and then to add an additional 750 to 1000 FTU/kg to the diet to destroy phytate without making any further formulation changes. Using this approach, the matrix from the first 500 FTU/kg would already make an adjustment in the mineral content of the diet, helping reduce diet costs and ensuring a balanced supply of digestible minerals to the bird, while the extra enzyme will mainly destroy dietary phytate and boost the poultry performance.


Tiago Tedeschi dos Santos

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