## 4 Discussions
[6] reported that the highest phytase doses (3000-12,500 phytase activity units, FYT/kg), much higher than the recommended ones, could increase ADG in the experimental group up to the values obtained using an adequate phosphorus diet or even could somewhat surpass those valued. By contrast, the standard phytase dose (250-1000 FYT/kg) has no effect at this life period, although it is quite efficient for young animals. At the late period, in the group with the low-phyrase diet, the slaughter weight of barrows was almost the same as those in the group with a phosphorus-deficient diet. The efficacy of low phytase doses in the broilers' feed is slightly higher than that in the feed of barrows [26]. Our data do not quite agree with the conclusions in the references because we found no substantial influence of the conventional phytase, even if its dose increased from 100 FYT/kg to 1000 FYT/kg. Therefore, the dose of 3000-12,500 recommended by [PERSON] et al. [25] and [PERSON] et al. [6] looks unreasonable. The difference in the recommended doses may be caused by different approaches to diet composition. All the referenced authors performed their trials using a well-balanced diet with either a faint or non-existent phosphorus deficit. By contrast, we used an original diet without bone meal based on grain only to make the effect of the phytase more pronounced. The final body weight in the negative control group was 20% less than that in the positive control group, where the phosphorus deficit was compensated with 0.5% disodium pyrophosphate dehydrate; this could confirm the conclusion. This fact shows that the phosphorus deficit was indeed the crucial nutritional factor limiting the chickens' growth. The application of the encapsulated OPP to the diet increased the chickens' growth rate to the level of that in the positive control group or even higher. In turn, using conventional phytase at either dose increased the growth rate by 5-6% only compared to the 20% difference between the positive and negative control groups. The data show a qualitatively better effect of the encapsulated phytase compared to the free enzyme, which cannot be compensated by increasing doses. On the other hand, the encapsulated OPP at a dose of 15 FYT/kg was much less efficient than at a dose of 30 FYT/kg and demonstrated efficacy comparable to the conventional phytase from _A. ficuum_ at doses of both 100 and 1000 FYT/kg. This makes us suppose that the encapsulated OPP is effective only within narrow dose range. This shortcoming could be practically important because the molar activity of the encapsulated phytase is low, and a feed yeast overdose may impact chickens unfavourably. It is worth noting that the best FCR values reached in our study (the positive control group and the group 'OPP at a high dose of 30 FYT/kg') are substantially higher than the reported ones in the literature [6; 25]. The elemental analysis of the chicken faeces from the positive and negative control groups demonstrates that the amount of accessible phosphorus, which is most responsible for difference in the growth rate between these groups, is relatively small compared to the total phosphorus amount in the diet. This conclusion is confirmed by the direct assay of the phosphorus in the negative and positive control group diets. Applying the encapsulated phytase nearly halves the residual phosphorus in the faeces compared to both control groups. In our opinion, this is a key argument in favour of the high efficacy of encapsulated phytase in the intestinal tract of the broilers, unlike that of the free enzyme. Along with the phosphorus release, the encapsulated OPP at a high dose of 30 FYT/kg significantly decreases the residual contents of valuable macro- and microelements, namely Mg, K, Ca,Zn, and Cu. This observation, presumably caused by the anti-nutritional effect of the grain phytase on the colon absorption, explains why the chicken growth rate at a high dose of 30 FYT/kg can be even higher than that in the positive control group.