True Total-Tract Digestibility of Calcium in Limestone and Dicalcium Phosphate for Twenty-Kilogram Pigs Are Additive in a Semi-Purified Diet

The objective of this study was to test the additivity of true total tract digestibility (TTTD) for calcium (Ca) in limestone and dicalcium phosphate for 20-kg pigs. Seventy-two barrows with an average initial BW of 20.8 ± 1.3 kg were blocked by weight and randomly assigned to 9 dietary treatments in a 3 × 3 factorial arrangement of three Ca sources included limestone, dicalcium phosphate, and their mixture at a ratio of 1:1; and dietary Ca concentration at 4.0, 5.0, and 6.0 g/kg. Potassium phosphate was added to adjust the dietary phosphorus level and maintain a 1.0:1 total Ca: total P ratio. Diets was fed for a 5-d adjustment period followed by a total collection period of 5 d with chromium oxide and ferric oxide as a markers to determine the initiation and termination of fecal collection respectively. Data were analyzed using GLM procedure of SAS as a randomized complete block design in a 3 × 3 factorial arrangement. The results showed the increased Ca concentration linearly increased (P< 0.001) Ca intake, fecal Ca output, and Ca absorbed, but no effect on apparent total tract digestibility of Ca within each Ca sources. The average apparent total tract digestibility was 66.46, 70.34, and 69.32% for limestone, dicalcium phosphate, and their mixture, respectively. By regressing daily digested Ca against daily Ca intake, the TTTD of Ca was determined at 70.06, 76.42, and 73.72% for limestone, dicalcium phosphate, and their mixture, respectively. And no difference was observed using confidence intervals derived from standard errors of respective regression coefficients. The calculated TTTD for Ca in limestone and dicalcium phosphate mixture was calculated to be 72.67% based upon the Ca contribution coefficient calculated to be 0.590 for limestone and 0.410 for dicalcium phosphate. The calculated Ca TTTD (72.67%) in the mixture was not statistically different from the determined Ca TTTD (73.72%). In conclusion, the TTTD for Ca in limestone and dicalcium phosphate are additive in the semi-purified diet for pigs.