Effects of standardized total tract digestible phosphorus on growth performance of 11- to 23-kg pigs fed diets with or without phytase,

Carine M. Vier, Steve S. Dritz, Fangzhou Wu, Mike D. Tokach, Joel M. DeRouchey, Robert D. Goodband, Márcio A.D. Gonçalves, Uislei A.D. Orlando, Jason C. Woodworth

Two experiments were conducted to determine the standardized total tract digestible phosphorus (STTD P) requirement for 11- to 23-kg nursery pigs fed diets with or without phytase. A total of 1,080 and 2,140 pigs (PIC 359×Camborough, Hendersonville, TN; initially 11.4 ± 0.29 and 11.1 ± 0.24 kg) were used in Exp. 1 and 2, respectively. There were 23 to 27 pigs per pen with 6 and 12 replicate pens per treatment in Exp. 1 and Exp. 2, respectively. After weaning, pigs were fed a common pelleted diet with 0.45% STTD P for 7 d, and a common phase 2 meal diet with 0.40% STTD P for 14 d in Exp. 1 and 18 d in Exp. 2. Pens of pigs were then were allotted to dietary treatments in a randomized complete block design with body weight (BW) as the blocking factor. In Exp. 1, dietary treatments consisted of 0.26, 0.30, 0.33, 0.38, 0.43, 0.48 and 0.53% STTD P. Treatments were achieved with the inclusion of monocalcium phosphate at the expense of corn. In Exp. 2, diets contained 1,000 phytase units (FYT; Ronozyme Hiphos 2500, DSM Nutritional Products, Inc., Parsippany, NJ) with assumed release value 0.132% STTD P, and treatments consisted of 0.30, 0.33, 0.38, 0.43, 0.48, 0.53 and 0.58% STTD P. These STTD P concentrations included the expected phytase release of 0.132% STTD P. In both experiments, a similar 1.17:1 Ca:P ratio was maintained across treatments. Statistical models included linear model (LM), quadratic polynomial (QP), broken-line linear (BLL), and broken-line quadratic (BLQ). In Exp. 1, increasing STTD P increased (linear, P < 0.001) ADG, ADFI, G:F, final BW, grams of STTD P intake per day and per kilogram of gain. There also was a marginal quadratic response for G:F (P < 0.066). In Exp. 2, ADG and G:F increased quadratically (P < 0.05), while ADFI increased linearly (P = 0.060) with increasing STTD P. The BLL and QP model provided similar fit to G:F in Exp. 1, estimating the requirement for maximum G:F at 0.34 and 0.42%, respectively. The BLL was the best fitting model for ADG and G:F in Exp. 2, estimating the breakpoint at 0.40 and 0.37% STTD P, respectively. The BLL andBLQ models estimated the breakpoint for ADG as a function of STTD P intake in g/d at 2.92 and 3.02 g/d, respectively. These data provide empirical evidence that for 11- to 23-kg pigs, the NRC (2012) accurately estimates the STTD P requirement on a g/d basis. As a percentage of the diet, the STTD P requirement for diets without or with 1,000 FYT added phytase ranged from 0.34 to 0.42%.