Meat and bone meal (MBM) is a product of the rendering industry composed primarily of the offal and bones of slaughtered livestock, fat from unmarketable animal tissues, unsellable retail meat products, and whole condemned carcasses (excluding hair, blood, hooves, horns, and contents of the gastrointestinal tract).  MBM is traditionally used as an animal protein source in swine diets, but because of its high concentrations of calcium and phosphorus, it can also replace inorganic phosphates in swine diets.

The proportions of soft tissue and bone in different sources of MBM can vary widely. Because mineral digestibility differs in bone and soft tissue, the variation in composition of MBM sources leads to a variation in mineral digestibility values.

An experiment was conducted to 1) determine the apparent (ATTD) and standardized (STTD) total tract digestibility of phosphorus and the ATTD of calcium in 8 different sources of MBM,  2) estimate variation among MBM sources, and 3) develop equations to predict the concentrations of digestible phosphorus and calcium in MBM.

A total of 72 growing pigs with an average initial body weight of 18.0 kg were fed one of nine dietary treatments. Eight of the diets were formulated to contain primarily cornstarch and sucrose, with 8% consisting of one of the sources of MBM. The last diet was a phosphorus-free diet that was used to measure the basal endogenous losses of phosphorus. MBM was the only source of phosphorus and calcium in the eight experimental diets.

The ATTD (%) of phosphorus and calcium in each diet were calculated according to the following equation: 

ATTD (%) = [(P_intake − P_feces)/P_intake] × 100

STTD of phosphorus was calculated by correcting ATTD values for the basal endogenous loss.

The composition of the eight different MBM samples is shown in Table 1. Two of the samples that were used in this experiment had P concentrations less than 4.0%. These samples would, therefore, be considered meat meal according toAssociation of American Feed Control Officials (AAFCO) definitions.

The concentration of phosphorus in the samples ranged from 2.6 to 5.6%, with a coefficient of variation (CV) of 19.5%. The phosphorus:ash ratios were relatively consistent, ranging from 0.13 to 0.16 (CV = 7.8%). The concentration of calcium ranged from 5.4 to 11.8% with a CV of 21.1. However, the calcium:ash (0.25 to 0.34) and calcium:phosphorus (1.95 to 2.14) ratios in the samples were relatively consistent (CV = 8.8 and 3.0%, respectively).

The daily amount of phosphorus absorbed differed (P < 0.05) from 0.96 to 1.58 g/d among the eight MBM sources. The ATTD of phosphorus differed (P < 0.05) from 52.1 to 80.1%, with an average of 65.9 ± 8.8%. The STTD of phosphorus differed (P < 0.05) from 54.8 to 84.4%), with an average of 68.8 ± 9.3%.

The STTD of phosphorus in MBM decreased with increasing concentrations of ash, calcium, and phosphorus. Between 61 and 72% of the variability in STTD values in MBM was explained by differences in the concentrations of these three components. This indicates that greater proportions of bone in MBM will lead to lower STTD values because the phosphorus in bone is less digestible by pigs than the phosphorus in soft tissue.

The final prediction model for STTD of phosphorus (%) in MBM was:

STTD of P (%) = 66.345 + 4.225 × ash – 13.126 × Ca (R² = 0.83, RMSE = 4.61; P < 0.01).

The daily amount of calcium absorbed differed (P < 0.05) from 1.99 to 3.15 g/d among pigs fed the different MBM sources, and the ATTD of calcium differed (P < 0.05) from 53.0 to 81.4%, with an average of 65.1 ± 9.2%.

The final prediction model for ATTD of Ca (%) in MBM was:

ATTD of Ca (%) = 67.316 + 3.833 × ash – 12.398 × Ca (R² = 0.87, RMSE = 3.97; P = 0.01).

• The composition of meat and bone meal varies significantly among different sources, as do the concentrations of phosphorus and calcium.
• The digestibility of minerals in soft tissue differs from the digestibility of minerals in bone. This means that the digestibility of minerals in a particular source of MBM will vary depending upon the composition of the source. Thus, there is no single figure for phosphorus or calcium digestibility in MBM, and it is important to be able to estimate digestibility values for a given source.
• Prediction equations using the concentrations of ash and minerals may be used to estimate phosphorus and calcium digestibility in MBM fed to growing pigs.

Table 1. Analyzed chemical composition (as-fed basis) of the meat and bone meal (MBM) sources

Table 2.Apparent total tract digestibility (ATTD, %) and standardized total tract digestibility (STTD, %) of P in 8 different meat and bone meal (MBM) sources fed to growing pigs