True digestible phosphorus requirement of grower pigs

The objective of this research is to determine the true total tract digestible P requirement for 4 BW categories of pigs: 10 to 20, 20 to 40, 40 to 60, and 60 to 80 kg. The true total tract digestible P content was calculated based on the determined TTTD of P in corn, SBM, and monocalcium phosphate. To determine the TTTD of P in corn and SBM, 54 barrows with an average initial BW of 14.7 ± 1.6 kg were used in a randomized complete block design with a 3 × 2 factorial arrangement of 6 diets. These 6 diets were established by the combination of 3 P sources (corn, SBM, and their mixture at a ratio of 2:1) and 2 P levels (low and high). The diets were fed for a 5-d adjustment period followed by a total sample collection period of 7 d with ferric oxide as a marker to determine the initiation and termination of fecal collection. The results showed the high dietary P level increased P intake, fecal P output, and digested P compared with low dietary P level (P \u3c 0.001). Regressing daily digested P against daily P intake, the TTTD of P was estimated at 40.53, 35.96, and 37.52% for corn, SBM, and their mixture, respectively. The expected TTTD of P in corn and SBM mixture was calculated to be 37.92%, which was not statistically different from the determined value (37.52%). The TTTD of P in monocalcium phosphate was determined using 48 15-kg barrows and 24 25-kg barrows. The pigs were used in a randomized complete block design with 6 replicate pigs per dietary treatment. For 15-kg (15.7 ± 1.53 kg) pigs, 8 dietary treatments were established by incremental addition of 3.5 g/kg of monocalcium phosphate to a corn-SBM-based diet (3.30 g/kg total P), while 4 dietary treatments for 25-kg (25.2 ± 1.04 kg) pigs were constituted by incremental addition of 2.4 g/kg of monocalcium phosphate to a corn-SBM-based diet (2.96 g/kg total P). Limestone was added accordingly to maintain a constant Ca:P ratio of 1.25:1 across all diets. A 5-d adjustment period preceded a 5-d total collection of feces, and ferric oxide was used as a marker to time the initiation and termination of fecal collection. The results showed that dietary P intake, fecal P output, and digested P increased linearly (P \u3c 0.05) with the increasing supplementation of monocalcium phosphate for both groups of pigs. The regression of daily digested P against daily P intake gave a TTTD of 67.5% for P in monocalcium phosphate for 15 kg pigs and of 84.3% for 25 kg pigs. The true digestible P requirement of grower pigs was determined in the last four studies. One hundred and eight barrows and gilts in 4 BW categories of 10 to 20, 20 to 40, 40 to 60, and 60 to 80 kg (initial BW 9.7 ± 0.77, 20.1 ± 1.24, 40.6 ± 1.59, and 57.4 ± 3.35 kg, respectively) were used. Each group of pigs were fed diets for 3 wk. Monocalcium phosphate was added to a corn-SBM-based diet to establish 6 levels of TTTD-based digestible P, ranging from 1.55 to 4.21 g/kg of diet for 10 to 20 kg pigs, from 1.31 to 4.64 g/kg for 20 to 40 kg pigs, from 1.26 to 3.98 g/kg for 40 to 60 kg pigs, and from 1.21 to 3.31 g/kg for 60 to 80 kg pigs. Limestone was added accordingly to maintain a constant Ca concentration across all diets. The growth performance of the pigs was improved with the increasing concentration of digestible P. The broken-line regression model explained more than 90% of the total variance. Based on broken-line regression, the true digestible P requirement for 10 to 20 pigs with barrows and gilts mixed at the ratio of 1:1, was estimated to be 3.22 g/kg of diet (887 g DM/kg) for pigs when G:F of the overall duration was used as a response variable. Using ADG, the corresponding P requirement was 3.19 g/kg of diet. The corresponding estimates of true digestible P requirement were 3.03 and 3.09 g/kg of diet (879 g DM/kg) for 20 to 40 kg pigs, 2.67 and 2.66 g/kg of diet (884 g DM/kg) for 40 to 60 kg pigs, and 2.33 and 2.29 g/kg of diet (884 g DM/kg) for 60 to 80 kg pigs using G:F and ADG as a response variable, respectively. (Abstract shortened by UMI.