An in vitro method to determine phosphorus digestibility of rainbow trout Oncorhynchus mykiss (Walbaum) feed ingredients

An in vitro method was developed to assess the digestibility of phosphorus in 12 plant and animal feed ingredients for rainbow trout Oncorhynchus mykiss (Walbaum). The method simulates the gastrointestinal tract of the rainbow trout with regard to pH and gastrointestinal enzymes. Phosphorus solubility was measured after acid digestion (pH 3) with and without gastric enzymes, after alkaline digestion (pH 9) with and without intestinal enzymes, and after a two‐step process involving acid and alkaline digestion. Commercially available digestive enzymes from mammals were compared with digestive enzymes from rainbow trout. Correlating in vitro digestibility with in vivo digestibility showed that acid digestion with both commercial enzymes (r2=0.98, P