Effects of Standardized Total Tract Digestible Phosphorus on Growth Performance, Carcass Characteristics, Bone Mineralization, and Economics of 53- to 287-lb Pigs

A total of 1,130 barrows and gilts (PIC; 359 × Camborough, initial pen average BW of 53.2 ± 1.61 lb) were used in a 111-d growth trial to determine the standardized total tract digestible (STTD) P requirement of growing-finishing pigs from 53 to 287 lb. Pens of pigs were randomly assigned to 1 of 6 dietary treatments in a randomized complete block design with BW as a blocking factor. There were 7 replicate pens per treatment and 26 to 27 pigs per pen (at least 13 barrows and gilts per pen). The experimental diets were corn-soybean meal-based and were fed in 4 phases. The 6 dietary treatments were formulated to contain 80, 90, 100, 115, 130, and 150% of the NRC publication STTD P requirement for growing-finishing pigs within each phase. The STTD P levels were achieved by increasing the amount of limestone and monocalcium phosphate at the expense of corn, maintaining a similar 1.14 to 1.16:1 total Ca:P ratio across treatments, with no added phytase. Overall, increasing STTD P resulted in a quadratic response in ADG, F/G, and final BW (P \u3c 0.05). The greatest improvement was observed with STTD P at 130% of NRC for ADG and final BW and 115% STTD P of the NRC recommendation for F/G. Average daily feed intake increased linearly with the inclusion of STTD P (P \u3c 0.05). Increasing STTD P resulted in a linear increase in fat-free bone ash weight and percentage ash (P \u3c 0.05). Barrows had significantly higher percentage ash compared to gilts (P \u3c 0.05). Increasing STTD P resulted in an increase in HCW and carcass ADG, with the greatest response observed with STTD P at 130% of NRC (quadratic, P \u3c 0.05). There was a marginally significant quadratic response in carcass F/G, with the greatest improvement with STTD P at 115% of NRC (P \u3c 0.10). Carcass yield decreased with increasing STTD P (linear, P \u3c 0.05), while there was a marginally significant decrease in backfat and increase in fat-free lean (linear, P \u3c 0.10). No difference was observed for loin depth (P \u3e 0.05). Feed cost per pig increased linearly with increasing STTD (P \u3c 0.05). Contrarily, gain value per pig and IOFC increased quadratically, with the greatest profit observed with STTD P at 130% of NRC (P \u3c 0.05). For ADG and feed efficiency, the quadratic model demonstrated the best fit. The maximum response in ADG was estimated at 122% of NRC STTD P, and the maximum response in feed efficiency was estimated at 116% of NRC STTD P. The broken-line linear model best fitted the data for ash as a percentage of fat-free dried bone, with a plateau achieved at 131% of the NRC STTD P requirement. In conclusion, the estimated STTD P requirement for growing-finishing pigs from 53 to 287 lb ranged from 116 to 131% of the NRC publication recommendations for each phase, depending on the response criteria and statistical model