Digestibility of phosphorus and calcium in meat and bone meal fed to growing pigs

Seventy-two growing pigs (initial BW: 18.0 ± 1.6 kg) were used to determine the apparent total tract digestibility (ATTD) of P and Ca and the standardized total tract digestibility (STTD) of P in 8 different sources of meat and bone meal (MBM) and to develop equations to predict digestibility of P and Ca in MBM. Pigs were housed individually in metabolism cages and were randomly allotted to 9 diets with 8 replicate pigs per diet. Eight diets were formulated by mixing cornstarch, sucrose, soybean oil, sodium chloride, vitamin-mineral premix, and 8% of each source of MBM, and MBM was the sole source of P and Ca in each diet. A P-free diet was used to measure basal endogenous P losses (EPL) by the pigs. Feces were collected for 5 d based on the marker to marker approach after a 5-d adaptation period. On an as-fed basis, the concentration of P in the MBM sources ranged from 2.6 to 5.3% with an average of 4.3 ± 0.8% whereas Ca concentration ranged from 5.1 to 11.0% with an average of 9.2 ± 2.0%. The variation among MBM samples in Ca and P concentrations was calculated (CV = 22.1 and 20.0%, respectively) as was the variation in the concentration of other chemical components (CV = 6.2, 10.5, and 13.8% for CP, acid-hydrolyzed ether extract, and ash, respectively). The ATTD of P (52.1 to 80.1%, average = 65.9 ± 8.8%) and Ca (53.0 to 81.0%, average = 63.9 ± 9.4%) differed (P < 0.05) among MBM sources. The basal EPL was measured at 106 ± 51 mg/kg DMI in pigs fed the P-free diet. The STTD of P was different (54.8 to 84.4%; average = 68.8 ± 9.3%; P < 0.05) among MBM sources. The ATTD of Ca and the STTD of P decreased (P < 0.01) as ash, Ca, and P concentration in MBM increased, and the ATTD of Ca was positively related (R² = 0.99, P < 0.001) with the STTD of P. The STTD of P (%) in MBM may be predicted as 107.857 - 8.8 × total P [R² = 0.68, root mean square error (RMSE) = 5.73, P < 0.01] whereas ATTD of Ca (%) may be predicted as 105.375 - 9.327 × total P (R² = 0.75, RMSE = 4.70, P < 0.01). In conclusion, P and Ca digestibility varies among sources of MBM, but prediction equations using the concentration of total P in MBM may be used to estimate P and Ca digestibility in MBM fed to growing pigs.