bone ash, growth performance, nursery pigs, phosphorus, phytase


A total of 1,080 nursery pigs (PIC 280 ×1050, initially 13.0 ± 2.38 lb BW) were housed in 3 commercial research rooms and used in a 46-d study to determine the effects of increasing standardized total tract digestible (STTD) phosphorus (P) concentrations in diets with and without phytase on growth performance and percentage bone ash. Pens of pigs (10 pigs per pen, 9 pens per treatment) were balanced for equal pen weights and allotted randomly to 1 of 12 treatments. Dietary treatments were arranged in 2 sets of dose titration with 6 levels of STTD P with and without 2,000 phytase unit (FYT) of phytase (DSM Nutritional Products, Inc., Parsippany, NJ). The STTD P levels were expressed as percentage of the NRC (2012) requirement estimates (0.45 and 0.40% for phases 1 and 2, respectively) and were: 80, 90, 100, 110, 125, and 140% of NRC in diets without phytase and 100, 110, 125, 140, 155, and 170% of NRC in diets with phytase. Diets were provided in 3 phases, with experimental diets fed during phase 1 (d 0 to 11) and phase 2 (d 11 to 25), followed by a common phase 3 diet from d 25 to 46. On d 25, 1 median-weight gilt from each pen was euthanized and radius samples were collected for analysis of bone ash. During the treatment period (d 0 to 25), increasing STTD P from 80 to 140% of NRC in diets without phytase improved average daily gain (ADG) (quadratic, P = 0.005), average daily feed intake (ADFI) (quadratic, P = 0.043), and feed efficiency (F/G) (linear, P < 0.001; quadratic, P = 0.063). Estimated STTD P requirement in diets without phytase was 117 and 91% of NRC for maximum ADG according to quadratic polynomial (QP) and broken-line linear (BLL) models, respectively, and ranged from 102 to >140% of NRC for maximum feed efficiency using BLL, broken-line quadratic, and linear models. When diets contained phytase, increasing STTD P from 100 to 170% of NRC improved ADG (quadratic, P = 0.031) and F/G (linear, P = 0.005; quadratic, P = 0.065). Estimated STTD P requirement in diets containing phytase was 138% for maximum ADG (QP model) and was 147 (QP model) and 116% (BLL model) of NRC for maximum feed efficiency. Increasing STTD P increased (linear, P < 0.001) percentage bone ash regardless of phytase addition. Comparing diets containing the same STTD P levels, adding phytase improved (P < 0.001) ADG, ADFI, and F/G. In summary, estimated STTD P requirements varied depending on the response criteria and statistical models and ranged from 91 to >140% of the NRC in diets containing no phytase, and from 116 to >170% of NRC for diets containing 2,000 FYT phytase. The high dose of phytase promoted growth performance and improved the dose responses to dietary STTD P for ADG and feed efficiency in 13- to 28-lb nursery pigs.


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