True digestible phosphorus requirement for forty- to eighty-kilogram pigs

The objective of this study was to determine the true digestible P requirement of 40- to 60-kg (Exp. 1) and 60- to 80-kg (Exp. 2) pigs by broken-line analysis of growth performance data using 6 levels of true digestible P. In each 3-wk experiment, 108 barrows and gilts were used, and 6 levels of monocalcium phosphate were added to a corn-soybean meal-based diet to establish 6 graded levels of true total tract digestible P ranging from 1.26 to 3.98 g/kg of diet in Exp. 1 or from 1.21 to 3.31 g/kg in Exp. 2. The true digestible P content was calculated using true total tract digestibility of 40.53%, 35.96%, and 84.31% for P in corn, soybean meal, and monocalcium phosphate, respectively. Limestone was added accordingly to maintain a constant Ca level across all diets of each experiment. The results of Exp. 1 showed that with graded supplementation of monocalcium phosphate, ADG linearly increased ( < 0.001) in wk 1 and both linearly and quadratically increased ( < 0.01) in wk 2, wk 3, and wk 0 to 3, and G:F linearly improved ( < 0.001) in wk 1, quadratically improved ( < 0.05) in wk 3, and both linearly and quadratically improved ( < 0.05) in wk 2 and wk 0 to 3 ( < 0.05). In Exp. 2, ADG linearly increased ( < 0.001) in wk 1 and both linearly and quadratically increased ( < 0.05) in wk 2, wk 3, and wk 0 to 3, with the graded supplementation of monocalcium phosphate, and G:F linearly improved ( < 0.01) in wk 1 and wk 3 and both linearly and quadratically improved ( < 0.001) in wk 2 and wk 0 to 3. In Exp. 1, the true digestible P requirement was estimated to be 2.66, 2.79, and 2.51 g/kg of diet (884 g DM/kg) for pigs of mixed sex, barrows, and gilts, respectively, on the basis of broken-line regression of ADG data for wk 0 to 3 against 6 true digestible P levels. Using G:F, the P requirement estimate was correspondingly 2.67, 2.51, and 2.93 g/kg of diet. In Exp. 2, the true digestible P requirement was estimated to be 2.29, 2.20, and 2.39 g/kg of diet (884 g DM/kg) using ADG data for wk 0 to 3 as the response variable and to be 2.33, 2.19, and 2.47 g/kg using wk 0 to 3 G:F data for pigs of mixed sex, barrows, and gilts, respectively. In conclusion, the mean TTTD-based P requirement was 2.66 and 2.31 g/kg of diet (884 g DM/kg) for 40- to 60-kg and 60- to 80-kg pigs, respectively.