The objective of this study was to determine the standardized total tract digestible phosphorus (STTD P) requirement of nursery pigs from 11 to 23 kg fed diets containing 1,000 phytase units (FYT). A total of 2,140 barrows and gilts (PIC 359×Camborough, initial BW 11.1 ± 0.24 kg) were used in a 21-d growth trial with 24 to 27 pigs per pen and 12 pens per treatment in a randomized complete block design. The 7 dietary treatments consisted of 0.30, 0.33, 0.38, 0.43, 0.48, 0.53, and 0.58% STTD P, which represented 90, 100, 115, 130, 145, 160 and 175%, respectively, of the NRC (2012) requirement estimate for STTD P for pigs weighing 11 to 23 kg. All diets contained 1,000 FYT of Ronozyme Hiphos 2500 (DSM Nutritional Products, Inc., Parsippany, NJ) with assumed release values of 0.15% available P and 0.132% STTD P. Treatments were achieved by increasing the amount of calcium carbonate and monocalcium phosphate at the expense of corn, while maintaining a similar 1.17:1 total Ca:total P ratio across treatments. Experimental data were analyzed with pen as the experimental unit, using generalized linear and nonlinear mixed models, which included quadratic polynomial, broken-line linear, and broken-line quadratic models. Increasing STTD P quadratically improved (P < 0.05) ADG and feed efficiency (G:F). Final BW and ADFI increased linearly (P < 0.05) up to the highest STTD P level. Income over feed cost improved quadratically (P < 0.05), with the highest income observed at 0.43% STTD P. The broken-line linear plateau was estimated at 0.40% STTD P for ADG and at 0.37% STTD P for G:F. In conclusion, the estimated STTD P requirement for nursery pigs from 11 to 23 kg fed diets containing 1,000 FYT were greater than NRC (2012) requirement estimates and ranged from 0.37 to 0.43% to optimize performance and economic return.
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