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The practical P value (STTD P) of the phytase used in this study was determined by formulating three commercially relevant diets and to generate a final diet STTD P value as postulated in this study depending on phytase dose (Table 6).
Values for the STTD of P determined for each tested feed ingredient without the addition of phytase are in agreement with values reported in the literature ([3,21]; Table 2).
The phytase concentration (FTU/kg) needed to maximize the STTD of P in the tested feed ingredients determined by the best regression model (Table 4) is shown in Figures 1 to 6 for CM, corn, RB, SBM, SFM, and wheat.
The broken-line analysis has been used elsewhere to determine the phytase concentration needed to maximize the STTD of P in complete diets [9].
The results from this study indicate that the efficiency of phytase in improving the STTD of P varies among feed ingredients and this might be attributed, in part, to composition, level, and location of phytate within different plant-based feed ingredients [5].
Because phytase supplementation increases the STTD of P differently depending on the feed ingredient, it seems logical that the response to phytase supplementation also varies depending on diet composition.
In conclusion, our results demonstrate the effectiveness of this novel microbial 6-phytase expressed in Psedomonas fluorescens to improve the STTD of P in various feed ingredients commonly used in swine diets.
It was calculated that a minimum of 550 FTU/kg of phytase was needed to obtain a STTD of P at a plateau of 69.
The reason that the difference in digestibility was observed in ATTD but not in STTD is most likely due to the different P content in the experimental diets.
The STTD of P in the CE used in this experiment was less than the value reported by Almaguer et al.
In conclusion, values for the ATTD of P in CE and PKE were greater than that in CR, but the STTD of P among CE, PKE, and CR did not differ greatly.