Interpretive Summary: Heat processing increased the digestibility of phosphorus in soybean expeller, canola meal, and canola expeller fed to growing pigs

By: Dr. Emily Taylor

Over two-thirds of the total Phosphorus in plant-based ingredients used in swine diets are present as inositol hexakisphosphate, more commonly known as phytate, and is poorly available to the pig. Deficient Phosphorus levels can have adverse effects on growth performance and the eutrophication of water. The current study published in the Journal of Animal Science evaluated heat processing to increase Phosphorus availability. More specifically, scientists determined the apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of Phosphorus in soybean expeller (SBE) and investigated the effects of heat treatment on ATTD and STTD of P in SBE, canola meal (CM), and canola expeller (CE) fed to growing pigs. 

Thirty-six barrows were assigned to 1 of 6 experimental diets, formulated with autoclaved, or non-autoclaved SBE, CM, and CE as the sole source of P.  Pigs fed Phosphorus sources that were autoclaved had an increase in both ATTD and STTD, with SBE diets being greater than both CM and CE diets. The authors suggested that the hydrolysis of inositol phosphates via heat processing might be more effective for the five or fewer phosphate groups to release free Phosphorus, leading to more available Phosphorus for digestion.  

In addition, heat treatment also increased the ATTD of Ca. Phytic acid will bind to Ca cations and form Ca-phytate complexes, thus reducing the ATTD of Ca in feed ingredients. Calcium increasing in ATTD as a result of heat treatment indicates that heat treatment may reduce Ca-phytate complexes, and in turn, increases the content of free Ca forms – increasing the digestibility of Ca. 

In conclusion, heat treatments do increase the Phosphorus availability in SBE, CM, and CE. However, the study had limitations, as concentrations of five or fewer phosphate groups were not analyzed. Therefore, further research is required to investigate the effects of heat treatment on lower groups of inositol phosphates.

This article is now available in the Journal of Animal Science.