Phosphorus fractions of various feedstuffs and apparent phosphorus availability to channel catfish

This study was conducted to determine different phosphorus fractions in corn, cottonseed meal, dehulled soybean meal, fish meal analog, meat-bone meal, fish meal from menhaden Brevoortia spp., rice bran, sorghum, wheat, and wheat middlings, and phosphorus availability of these feedstuffs to channel catfish Ictalurus punctatus. Test diets consisting of a 70:30 mixture of reference diet to test ingredient were used with chromic oxide as the nondigestible marker. The various test diets were fed for 5 d in triplicate to groups of channel catfish weighing approximately 150-200 g, and the fecal samples were obtained by stripping approximately 12 h after feeding. Feed and fecal samples were analyzed for total phosphorus (TP) and soluble reactive phosphorus (SRP), from which apparent availability coefficients were calculated. Apparent availability of SRP exceeded 92% for all ingredients, except menhaden fish meal (61%) and wheat (44%). Total phosphorus availability from animal products was variable: 47% for menhaden fish meal, 54% for meat-bone meal, and 92% for fish meal analog. Plant products also had variable TP availability values: 33% for corn, 35% for both sorghum and soybean meal, 51% for rice bran, 66% for cottonseed meal, 77% for wheat middlings, and 83% for wheat. These phosphorus availability values obtained for the various feedstuffs may allow formulation of diets that are better utilized by channel catfish and reduce phosphorus excretion.