Effects of particle size, ash content, and processing pressure on the 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. Three experiments were conducted to determine whether particle size, ash content, or processing pressure of MBM influences the bioavailability of P. Each experiment involved six replications of six treatments with individually penned pigs initially averaging 13 to 17 kg of BW. A low-P basal diet was fed with or without 0.1 or 0.2% added P (as-fed basis) from monosodium phosphate (MSP) or with three types of MBM added at levels that supplied 0.2% P (as-fed basis). The Ca level was 0.70%, and the lysine level was 0.95% in all diets. Pigs were allowed to consume their diets (meal form) on an ad libitum basis. At the end of the study, pigs were killed, and femurs and third and fourth metacarpals and metatarsals were removed for determination of breaking strength and ash content. Bone traits were regressed on added P intake for each P source, and slope-ratio procedures were used to estimate the bioavailability of P in MBM relative to that in MSP. In Exp. 1, a blended source of MBM ground to three particle sizes (amount that passed through 6-, 8-, or 12-mesh screens) was evaluated. In Exp. 2, low-ash MBM of porcine origin, high-ash MBM of bovine origin, and a 1:1 blend of the two sources were assessed. In Exp. 3, normally processed MBM was subjected to an additional 2.1 and 4.2 kg/cm2 of pressure for 20 min to determine whether excessive heat treatment would influence the bioavailability of P. Fineness of grind of MBM or processing pressure did not influence the relative bioavailability of P in this study; however, ash content of MBM affected P bioavailability. The relative availability of P in low-ash MBM of porcine origin (with composition typical of meat meal) was approximately 15 percentage units less than that in high-ash MBM of bovine origin. Overall, the bioavailability of P in MBM, relative to that in MSP, averaged 85%.