270 Interactive effects of available phosphorus and Ca:P on growth performance of nursery pigs fed diets containing phytase

Abstract An experiment was conducted to determine the interactive effects of available phosphorus (aP) and Ca:P on growth performance of nursery pigs. A total of 2,492 pigs PIC 337 × 1050, initial body weight (BW) = 5.6 kg, placed in pens with 35 or 36 pigs each, were used in a 36-d trial. Treatments were arranged as a 2 × 4 factorial structure with two levels of aP (0.40 or 0.55%) and four Ca:P (0.85, 1.07, 1.29, and 1.51) with 9 replicates per treatment. Four basal diets with the extreme aP and Ca:P levels were manufactured in meal form and blended at the farm to create intermediate treatments. Phytase Allzyme Spectrum Swine (Alltech, Nicholasville, KY) was included in the experimental diets at superdose levels with an estimated 0.15% aP release. The experimental diets were fed from d 0 to 19 and a common corn-soybean meal-based diet with adequate aP and 1.20 Ca:P was fed from d 19 to 36. Data were analyzed with the MIXED procedure in SAS in a randomized complete block design with pen serving as the experimental unit and initial BW as the blocking factor. There was no evidence (P 0.10) for aP and Ca:P interactive effects on growth performance (Table 1). From d 0 to 19, there was no evidence (P 0.10) for growth performance differences between the aP levels. Increasing Ca:P resulted in a quadratic response (P = 0.043) in gain to feed ratio (G:F), with no evidence for (P 0.10) differences in average daily gain (ADG) or average daily feed intake (ADFI). From d 19 to 36, pigs previously fed 0.55% aP had improved (P ≤ 0.047) ADFI and ADG. Pigs previously fed increasing Ca:P had improved (linear, P = 0.024) G:F. There was also no evidence (P 0.10) for interactive effects on removal or mortality rates. However, pigs fed greater aP had decreased (P = 0.021) mortality rate. In summary, there were minor performance differences between different aP and Ca:P levels, but feeding greater aP diets resulted in a significant improvement in mortality rate.