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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.
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.
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.
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Source: World Poultry, Vol. 27, No. 5
