In most plant feed ingredients, the majority of P is bound to phytate, which reduces digestibility of P in pigs, and therefore, the concentration of digestible P in these ingredients is relatively low. Phytate is negatively charged in the intestinal tract and can bind both endogenous and dietary nutrients, which results in precipitation of non-digestible nutrient-phytate complexes. Therefore, it is possible that the use of exogenous phytase can also increase the digestibility of other nutrients than P. As an example, addition of exogenous phytase to diets also releases Ca from phytate, and thus, increases the digestibility of Ca. However, it has not been conclusively demonstrated that phytase also increases the digestibility of energy-generating nutrients and other minerals in diets fed to pigs and inconsistent results among experiments have been reported. Therefore, the objective of this experiment was to test the hypothesis that increasing phytase dose increases the apparent total tract digestibility (ATTD) of minerals and gross energy (GE) in corn and soybean meal-based diets fed to growing pigs.

Experimental design

Forty-eight barrows (initial body weight: 22.61 ± 1.54 kg) were allotted to one of the 6 diets using a randomized complete block design with group as a block. Therefore, there were 8 replicate pigs per diet. Six diets based on corn and soybean meal were formulated. The first diet was the positive control (PC) diet that contained P at the requirement for standardized total tract digestible (STTD) P by 11 to 25 kg pigs (i.e., 0.33%; NRC, 2012). The second diet was the negative control (NC) diet that was similar to the positive control with the exception that no feed phosphates were used (STTD P in the NC diets = 0.16%). Four additional diets were formulated by adding 250, 500, 1,000, or 2,000 phytase units/kg to the negative control diet. The source of phytase was SuperPhy, which was supplied by Hanley International, LLC, Belmont, MA.

Feed provisions were recorded daily and diets were fed for 12 days. The initial 5 days were considered the adaptation period to the diet, and fecal materials were collected from feed provided during the following 4 days using the marker to marker procedure. Fecal samples were stored at – 20 °C immediately after collection.

The ATTD of GE and dry matter (DM) was calculated for each diet, and the concentration of DE in each diet was calculated as well.

Results

Feed intake of pigs was not affected by diet, but weight of feces was less (P = 0.005) if pigs were fed the PC diet than if pigs were fed the NC diet with no phytase, which resulted in greater ATTD of DM in pigs fed the NC diet with no phytase compared with the PC diet (Table 1). With no effect of diet on GE intake, the GE output was greater (P < 0.05) from pigs fed the PC diet, which resulted in less (P < 0.05) ATTD of GE and DE in the NC diet with no phytase compared with the PC diet. There was no effect of increasing phytase on the ATTD of GE and DE in the diets. Ash intake, ash concentration in feces, ash output, and absorbed ash were greater (P < 0.01) in pig fed the PC diet compared with the NC diet, but there was no difference in the ATTD of ash. As the level of phytase increases in the NC diets, the ATTD of ash linearly (P < 0.001) increased. Calcium intake, Ca output, absorbed Ca, and the ATTD of Ca in the PC diet were greater (P < 0.05) than in the NC diet with no phytase. Phosphorus intake, P output, absorbed P, and the ATTD and STTD of P were greater (P < 0.05) in the PC diet than in the NC diet with no phytase. However, as phytase level increased in the NC diets, the ATTD of Ca, ATTD of P, and STTD of P quadratically (P < 0.05) increased.

The ATTD of K, Na, Cu, Fe, Mn, and Zn did not differ between the PC and the NC diet with no phytase (Table 2). Values for the ATTD of K, Na, Cu, Fe, Mn, and Zn were not affected by the level of phytase. With similar intake, Mg output linearly (P = 0.036) decreased, which resulted in linear increases in the ATTD of Mg as phytase dose increased in the NC diets.

Key points

• The ATTD of DM and GE and concentration of DE in the NC diet were greater than in the PC diet if no phytase was used, but the ATTD of ash, K, Mg, Na, Cu, Fe, Mn, and Zn was not different between the 2 diets.
• There was no effect of increasing phytase on the ATTD of DM and GE or on the DE in the diets.
• As the level of phytase increased, the ATTD of ash, Ca, P, and Mg and the STTD of P increased, but the ATTD of K, Na, Cu, Fe, Mn, and Zn was not affected by the level of phytase.

Table 1. Effects of increasing phytase dose on ATTD of GE, DM, Ash, Ca, and P, and STTD of P in diets fed to growing pigs¹

      ¹Least square means represent 8 observations, respectively.

        ²PC vs. NC = comparing PC diet and NC diet with no phytase; Linear = linear effect of increasing phytase in NC diets; Quadratic= quadratic effect of increasing phytase in NC diets.

Table 2. Effects of increasing phytase dose on ATTD of macro and micro minerals in diets fed to growing pigs¹

       ¹Least square means represent 8 observations, respectively.

       ²PC vs. NC = comparing PC diet and NC diet with no phytase; Linear = linear effect of increasing phytase in NC diets; Quadratic= quadratic effect of increasing phytase in NC diets.