Blood meal and spray dried plasma protein are often included in diets fed to weanling pigs, and blood products are considered excellent sources of protein. The objective of this research was to measure apparent total tract digestibility (ATTD) and standardized total tract digestibililty (STTD) of phosphorus in spray dried animal plasma, porcine blood meal, and avian blood meal fed to weanling pigs. References such as the NRC typically provide relative bioavailability values for phosphorus rather than digestibility values. Relative bioavailability values, however, depend on the standard (e.g., monosodium phosphate or dicalcium phosphate) to which the availability is compared. Thus, these values are believed not to be additive in mixed diets. It is believed that STTD values are additive in mixed diets, and therefore will enable producers to formulate diets that accurately meet the phosphorus requirement of pigs without creating unneccesary excesses that are excreted in the manure.

Four diets were formulated. Three diets contained each of the three blood products. The fourth diet contained no phosphorus and was used to measure the basal endogenous phosphorus loss. Twenty-four weanling pigs (initial BW: 18.8 ± 3.2) were randomly allotted to the four diets. They were allowed to adapt to the diets for five days, and then feces were collected for five days. The collected feces were analyzed for phosphorus content, and STTD was calculated by subtracting endogenous phosphorus loss from the total fecal phosphorus output.

Blood products: excellent sources of digestible phosphorus

Feed intake was the same across the three experimental diets.  Pigs that were fed SDPP or porcine blood meal consumed more (P < 0.01) phosphorus than pigs that were fed poultry blood meal due to the latter's lower phosphorus concentration. Fecal phosphorus output was lower (P < 0.01) for pigs that were fed SDPP than for pigs that were fed porcine blood meal or poultry blood meal.  There were no differences in endogenous loss of phosphorus between the three dietary treatments. The ATTD of phosphorus was greater (P < 0.01) for pigs that were fed SDPP  than for pigs that were fed either porcine blood meal, which in turn had a greater (P < 0.01) ATTD of phosphorus than pigs that were fed poultry blood meal.

The STTD of phosphorus in pigs fed porcine blood meal or poultry blood meal was the same, and was less (P < 0.05) than the STTD of phosphorus in SDPP. The low concentration and high excretion of phosphorus in the poultry blood meal diet may have caused ATTD to be underestimated because endogenous phosphorus losses would make a relatively greater contribution to the fecal matter. However, this underestimation was corrected when values for STTD were calculated.

Key points

• Spray-dried plasma protein, porcine blood meal, and poultry blood meal are excellent sources of organic phosphorus.
• Spray dried plasma protein has a greater STTD of phosphorus than porcine or poultry blood meal. The STTD values indicate that phosphorus from spray dried plasma protein is completely digested, while phosphorus from porcine and poultry blood meal is almost completely digested.
• STTD values for phosphorus may be more additive in mixed diets compared with ATTD or relative bioavailability numbers, but more research is needed to confirm this assumption.

Table 1. Apparent total tract digestibility (ATTD) of P and Ca, and standardized total tract digestibility (STTD) of P in blood products

^a-c Means within a row lacking a common superscript letter differ (P < 0.05)

This research report is based on unpublished research by S. E. Boucher, R. C. Sulabo, and H. H. Stein.