True total-tract digestibility of phosphorus in monocalcium phosphate for 15-kg pigs.

The objective of this study was to determine the true total-tract digestibility (TTTD) of P in Ca(H(2)PO(4))(2) for 15-kg pigs using the regression technique. Forty-eight pigs (15.7 ± 1.53 kg initial BW) were used in a randomized complete block design. There were 8 dietary treatments with 6 replicates per treatment. The dietary treatments included a negative control (3.30 g/kg total P) and 7 additional dietary treatments with incremental addition of 0.74 g/kg P through Ca(H(2)PO(4))(2) resulting in a range of 3.30 to 8.45 g/kg total P in the dietary treatments. The ingredient composition of the negative control was 600 g/kg corn (Zea mays), 300 g/kg soybean (Glycine max) meal, 64.85 g/kg cornstarch, 20 g/kg soybean oil, 3.3 g/kg salt, 6.05 g/kg limestone, 3.0 g/kg vitamin + mineral premix, and 2.8 g/kg pure AA. Limestone was used to keep the Ca:P ratio constant at 1.25 across all dietary treatments and cornstarch was used to fill the slack. After a 5-d adaptation, total feces were collected for 5 d and were initiated and ended with the appearance of Fe(2)O(3)-marked feces. Daily feed allowance was set at between 3.5 and 4.0% of the BW of pigs to guarantee that the feed waste was minimized. Water was supplied separately at an allowance of 2 times the amount of feed. Dietary P intake, fecal P output, and digested P increased linearly (P < 0.001) with the increasing P level whereas the apparent total-tract P digestibility in diets increased both linearly (P < 0.001) and quadratically (P = 0.007). The regression of daily digested P against daily P intake gave an estimated TTTD of 67.5% for P in Ca(H(2)PO(4))(2) and the endogenous P losses were 494 mg/d. The R(2) with this linear regression was 0.93. In conclusion, a strong linear relationship was obtained between digested P and P intake; the TTTD of P in Ca(H(2)PO(4))(2) was 67.5% for 15-kg pigs.