Validation of an in vitro method for the estimation of apparent total tract digestibility of phosphorus in plant feed ingredients for pigs

The aim of this study was to validate an enzymatic in vitro method that estimates the apparent total tract digestibility (ATTD) of phosphorus (P) in feed ingredients from plant origin used in pig nutrition. Sixteen individually housed castrated male pigs (19.5 ± 2.9 kg) were fed a semisynthetic diet, either alone (control) or containing: wheat, barley, maize, potato protein concentrate, soybean expeller or rapeseed expeller for periods of 14 days. The ATTD of P was determined indirectly using celite as a marker. The in vitro released P was determined after three consecutive steps: preliminary soaking in acid medium, pepsin digestion in strong acid medium and pancreatin digestion in neutral medium. The in vivo ATTD of P were 0.21, 0.37, 0.48, 0.41, 0.33 and 0.39 in the respective feed ingredients as listed above. The in vivo ATTD of P and the in vitro released P were linearly correlated (in vitro released P = −0.118 (P>0.10) + 1.171 (P<0.01) × in vivo ATTD of P, R2 = 0.91). Thus, the in vitro method was successful in predicting in vivo ATTD of P in the plant feed ingredients tested here. The in vitro method can be proposed as an inexpensive tool to rapidly estimate ATTD of P in plant feed ingredients.