Dietary phytate may bind to proteins from feed ingredients by making indigestible nutrient-complexes. Therefore, it is possible that adding exogenous phytase to the diets increases digestibility of amino acids (AA). However, results of experiments in which microbial phytase has been added to diets fed to pigs have not consistently demonstrated increased ileal digestibility of AA. It is, however, possible that is because the dose of phytase was too low to obtain a positive effect on AA digestibility and that if greater doses were used, a positive response would be obtained. Therefore, the objective of this experiment was to test the hypothesis that super dosing four different sources of commercially available exogenous phytase increases the apparent ileal digestibility (AID) of CP and AA in a corn-soybean meal (SBM) based diet fed to growing pigs.

Experimental design

            Ten individually house barrows (initial BW: 75.16 ± 7.38) that had a T-cannula installed in the distal ileum were allotted to a replicated 5 × 5 Latin square design with 5 diets and five 7-d periods. The initial 5 d of each period was considered an adaptation period to the diets and ileal digesta were collected for 9 h on d 6 and 7.

            All experimental diets were formulated based on corn and soybean meal. The control diet did not contain exogenous phytase and contained approximately 70% of the Ca and P requirement (NRC, 2012). Four additional diets were formulated by adding 4 different sources of phytase (phytase A, B, C, and D at 2,500 units/kg diet) to the control diets. Vitamins and minerals except Ca and P were included in all diets to meet or exceed current requirement estimates (NRC, 2012). The statistical model included each diet as fixed effect and square, period, and pig as random effects.

Results

Results indicated that values for AID of DM, CP, and all AA except Ile, Phe, and Trp were not different among pigs fed the 5 diets (Table 1). The AID of Ile in the diet supplemented with phytase D was greater (P < 0.05) compared with the control diet, but there was no difference in the AID of Ile among pigs fed the control diet and the diets supplemented with phytase A, B, or C. The AID of Phe in the diets supplemented with phytase A or D was greater (P < 0.05) compared with the control diet, but there was no difference in the AID of Phe among pigs fed the control diet and the diets supplemented with phytase B or C. The AID of Trp in the diets supplemented with phytase C or D was greater (P < 0.05) compared with the control diet, but there was no difference in the AID of Trp among pigs fed the control diet and the diets supplemented with phytase A or B. For all other AA, no differences in digestibility were observed among treatments.

In conclusion, adding 2,500 units of phytase to diets containing corn and SBM did not affect values for the AID of DM, CP, and most AA.

Key points

• Pigs fed the diet supplemented with phytase D had greater values for the AID of Ile, Phe, and Trp compared with the control diet.
• Super dosing exogenous phytase did not affect the AID of DM, CP, and most AA in corn and SBM-based diets.

Table 1. Effects of super dosing phytase on AID of DM, CP, and AA in corn and SBM-based diets ¹