The impact of the interaction between dietary total phosphorus level and efficacy of phytase on the performance of growing-finishing pigs

Abstract

Two experiments were conducted to investigate the interaction between dietary total phosphorus (P) level and phytase on the performance of growing-finishing pigs. In experiment 1, a total of 96 growing pigs [Duroc × Landrace × Yorkshire (barrows, initial body weight (BW) = 39.1 ± 0.5 kg), 8 pigs per treatment] were used in a 5-d total fecal and urine collection study to determine the apparent total tract digestible (ATTD) P release value of phytase in 2 dietary standardized total tract digestible (STTD) P levels (1.49 vs 2.87 g/kg of STTD P) with 0, 250, 500, 750, 1000, and 1250 FTU/kg of phytase. The results indicated that there was an interaction between P level and phytase in the determination of coefficient of apparent total tract digestibility of P (P < 0.01). The determined P release curves were STTD P = −1.4 phytase2 × 10−6 + 20.8305 phytase × 10−3 + 6.88392 × 10−2, R² = 0.9766 [1] in low-P diets, and STTD P = −1.2 phytase2 × 10−6 + 20.2754 phytase × 10−3 + 1.86325 × 10−2, R² = 0.9965 [2] in high-P diets. In experiment 2, a total of 1344 growing pigs [Duroc × Landrace × Yorkshire (initial BW = 69.4 ± 0.6 kg), 28 pigs per pen] were used in a 35-d growth performance study. The study had 4 dietary treatments which included low-P (1.0 g/kg of STTD P) diet group, high-P (1.9 g/kg of STTD P) diet group, low-P diet + 1100 FTU/kg phytase group, and high-P diet + 250 FTU/kg phytase group. The two treatments with phytase were formulated to the same STTD P level using the P release value of phytase determined by equation [1] from Experiment 1. The results showed that the treatment with 1100 FTU/kg phytase had greater gain to feed ratio compared to the treatment with 250 FTU/kg phytase, 1.0 g/kg total STTD P group and 1.9 g/kg total STTD P group (P < 0.05). In conclusion, the determination of P release of phytase may be impacted by the total P level in the diet. The P release value determined in low-P diets may not be accurate for the diet formulation when dietary total P level is greater.