Performance and carcass traits of nursery, growing, and finishing pigs fed fourth-generation phytase superdoses in diets severely restricted in calcium and phosphorus

This study evaluated the effects of increasing inclusion levels of a bacterial phytase in diets with reduced calcium (Ca) and phosphorus (P) on growth performance and carcass traits of pigs across nursery, growing, and finishing phases. A total of 250 pigs (21 days of age; 6.079 ± 0.744 kg) were assigned to a randomized complete block design with five treatments: a positive control (PC), a negative control (NC; −0.18% available P and −0.16% Ca), and NC diets supplemented with 600, 1,200, or 1,800 FYT/kg. During the nursery phase, pigs fed the NC diet showed reduced average daily gain (ADG) and poorer feed conversion ratio (FCR) compared with PC (p < 0.05), whereas phytase supplementation restored performance to levels comparable to PC. Average daily feed intake was not affected (p > 0.05). In the growing and finishing phases, performance variables were affected by treatment (p < 0.05), with NC pigs showing lower ADG and worst FCR, while phytase-supplemented pigs performed similarly to PC. Across periods, quadratic responses to phytase inclusion were observed for FCR (p < 0.001), with estimated optimal levels of 1,320 and 1,404 FYT/kg during nursery and growing–finishing phases, respectively. Carcass traits were also affected by dietary treatments (p < 0.05). Pigs fed the NC diet showed lower final body weight (FBW), hot carcass weight (HCW), carcass yield (CY), and lean meat percentage (LMP) compared with PC, whereas phytase supplementation restored these variables to values comparable to PC. Quadratic responses to phytase inclusion were observed for FBW (p = 0.004), HCW (p < 0.001), CY (p = 0.028), and LMP (p < 0.001), with estimated optimal inclusion levels of 1,377, 1,324, 1,416, and 1,246 FYT/kg, respectively. In conclusion, phytase supplementation effectively mitigated the negative effects of dietary Ca and P restriction, maintaining growth performance and carcass characteristics comparable to a nutritionally adequate diet across all production phases.