Bioavailability of phosphorus in meat and bone meal for swine

Meat and bone meal (MBM), when supplemented with tryptophan, is an excellent protein source for pigs. It is also a rich source of Ca and P, but some research has suggested that the bioavailability of P is variable. Experiment I further examined the bioavailability of P in MBM. The MBM was obtained directly from a plant and was processed to pass through a 10-mesh screen. It contained 50.7% CP, 2.26% lysine,.10.0% Ca, and 5.0% P (air-dry basis). Individually penned pigs (n = 35; 17 kg initial BW) were fed (ad libitum basis) a low-P, corn-soybean meal-basal diet (0.95% lysine, 0.70% Ca, 0.34% P; as-fed basis) or the basal with graded levels of added P (0.067, 0.133 0.200%) from monosodium phosphate (MSP) or MBM for 40 d. The Ca level was 0.70% in all diets. Diets were fortified with salt, vitamins, and trace minerals. At terimnation, the third and fourth metacarpals and metatarsals and femurs were removed from all pigs. Growth rate and feed:gain improved linearly (P < 0.01) with P addition, regardless of source, whereas ADFI was unaffected (P = 0.20). Bone strength and ash increased linearly (P < 0.01) with increasing level of P from either source. The main effect of P source (MSP vs. MBM) was not significant, except for the greater femur strength (P < 0.05) in the pigs fed the MSP-supplemented diets. Femur and metacarpal/metatarsal strength and metacarpals ash (grams) were regressed on grams of added P consumed for each P source, with the basal included in both regressions. Based on slope ratios (MSP considered as 100%), the relative bioavailability of P in MBM averaged 87% when the regression lines were forced through a common intercept and 95% when unforced. In Exp. 2, 100 pigs were fed fortified corn-soybean meal or corn-soybean meal-MBM diets from 45 to 110 kg BW to evaluate MBM as the sole source of supplemental P. The MBM (54% CP, 2.3% lysine, 9.2% Ca, 4.4% P; air-dry basis) was substituted for corn and soybean meal on a lysine basis, and crystalline lysine was added to all diets at 0.15%. Tryptophan was included in diets containing MBM. Treatments were arranged in a 2 x 2 factorial with P source (dicalcium phosphate or MBM) and P level as the two factors. The two levels of P and Ca were at the NRC requirement or the NRC level plus 0.10% additional P and Ca. Performance, carcass traits, and bone strength were not affected by source of P and Ca, but bone strength was greater (P < 0.01) at the higher P and Ca level. These results indicate that the bioavailability of P in MBM, relative to that in MSP, is high (approximately 91%) for growing pigs, and MBM can serve as the sole source of supplemental P and Ca for finishing pigs.