Microbial phytase is usually included in diets for pigs to increase P absorption and utilization by hydrolyzing phytate within the gastrointestinal tract of pigs. High doses of phytase (i.e., > 1,000 FTU/kg) is also hypothesized to increase release of nutrients other than P due to increased degradation of phytate. A next generation biosynthetic bacterial 6-phytase (PhyG; DuPont Animal Nutrition) may increase digestibility of nutrients in diets for pigs; however, there are no data to demonstrate the efficacy of this phytase. Therefore, an experiment was conducted to test the hypothesis that the negative impact of phytate is reduced at higher phytase doses. It was also the objective of this research to test the hypothesis that inclusion of increasing levels of phytase increases bone ash and apparent total tract digestibility (ATTD) of minerals in diets containing varying phytate concentrations.

Experimental design

Three diets based on corn, soybean meal, and canola meal were formulated to contain 0.23%, 0.29%, or 0.35% phytate-bound P. Twelve additional diets were formulated by adding 500, 1,000, 2,000, or 4,000 phytase units (FTU)/kg of PhyG to the 3 basal diets. In addition, 3 reference diets were formulated by adding a commercial Buttiauxella phytase (PhyB) at 1,000 FTU/kg to the 3 basal diets containing no PhyG. All diets contained 0.40% titanium dioxide as an indigestible marker. A total of 144 growing pigs (initial body weight: 12.70 ± 4.01 kg) were randomly allotted to 18 diets with 8 replicate pigs per diet. Pigs were assigned to treatment groups using a randomized complete block design with 4 blocks of 36 pigs and 2 replicate pigs per diet in each block. Pigs adapted to diets for 15 d, and fecal samples were collected via anal stimulation on days 16, 17, 18, and 19. On the last day of the experiment (d 20), femurs were collected for bone ash analysis. Diets and fecal samples were analyzed for minerals and titanium to calculate ATTD of minerals.

Results

Diets containing 0.35% phytate-bound P had reduced (P < 0.01) ATTD of Ca, P, Mg, and K compared with diets containing 0.23% or 0.29% phytate-bound P, but inclusion of phytase increased (P < 0.01) ATTD of Ca, Na, and K (Table 1). Phytase increased ATTD of P and Mg, but to a greater extent in diets with 0.23 or 0.29% phytate-bound P, than in diets with 0.35% phytate-bound P, (interaction, P < 0.05). Diets containing 1,000 FTU/kg PhyG had greater ATTD of P (P < 0.05) than diets containing 1,000 FTU/kg PhyB. Phytase increased bone ash (g per femur), but to a greater extent if there was 0.35 rather than 0.23 or 0.29% phytate-bound P in the diets (interaction, P < 0.05).

Key points

• Phytate reduces mineral digestibility, but inclusion of phytase in the diets increased digestibility of Ca, P, Na, Mg, and K.
• The novel consensus phytase increased the ATTD of P and Mg to a greater extent in diets containing lower levels of phytate.
• The novel consensus phytase increased the ATTD of P in the diets more than the Buttiauxella phytase.
• The novel consensus phytase increased bone ash (g per femur) to a greater extend if pigs were fed diets with higher levels of phytate compared with lower levels of phytate.

Table 1. Apparent total tract digestibility (ATTD) of minerals and bone ash of pigs fed diets containing different concentrations of phytate-P and phytase dose¹

¹Data are least squares means of 6 to 8 observations per treatment.

²Contrasts between diets containing 1,000 FTU/kg from PhyG or PhyB.

^a-hMeans within a row lacking a common letter are different (P < 0.05).