264 Effects of increasing available phosphorus for 6 to 16 kg pigs fed diets containing phytase

Abstract An experiment was conducted to determine the effects of increasing available phosphorus (aP) levels on growth performance of nursery pigs under commercial conditions. A total of 2,340 pigs PIC 337 × 1050, initial body weight (BW) = 6.0 kg, placed in pens with 35 or 36 pigs, were used in a 39-d trial. Treatments were arranged in a dose titration with six levels of aP and 11 replicates per treatment. The aP levels were 0.33, 0.39, 0.46, 0.52, 0.59, and 0.65%. Two basal diets with the least and greatest aP levels were manufactured in meal form and blended at the farm to create the intermediate levels. Phytase Allzyme Spectrum Swine (Alltech, Nicholasville, KY) was included in the experimental diets at superdose levels with an estimated 0.15% aP release. Calcium levels were adjusted in each diet to maintain a constant 1.20 Ca:P. The experimental diets were fed from d 0 to 21 and a common corn-soybean meal-based diet with adequate aP level was fed from d 21 to 39. 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. From d 0 to 21, pigs fed increasing levels of aP had improved (quadratic, P ≤ 0.024) average daily gain (ADG), average daily feed intake (ADFI), and feed efficiency gain to feed ratio (G:F); Table 1. For ADG and G:F, the quadratic polynomial resulted in the best fit predicting 100% of maximum response at 0.50 and 0.52% aP for ADG and G:F, respectively. Similar improvements (quadratic, P ≤ 0.049) were also observed in the overall period (d 0 to 39). From d 21 to 39, while pigs were fed a common diet, there was no evidence (P 0.05) for differences in growth performance. There was no evidence (P 0.05) for differences in mortality rate. However, there was a quadratic response (P = 0.008) in removal rate, with declining rates up to 0.59% aP. In summary, growth performance of 6 to 16 kg pigs was maximized with 0.50 to 0.52% aP with further improvements in removal rate observed with greater aP levels.