The sparing effect of phytase in plant-protein-based diets with decreasing supplementation of dietary NaH2PO4for juvenile yellow catfishPelteobagrus fulvidraco

Abstract

An 8-week feeding trial was conducted to evaluate the sparing effect of dietary phytase on decreasing supplement of dietary sodium dihydrogen phosphate (NaH2PO4) in the diets of juvenile yellow catfish Pelteobagrus fulvidraco. Seven diets were formulated: one reference group that contained only 2% NaH2PO4; one control group that consisted of neither NaH2PO4 nor phytase; and five treatment groups supplemented with 1000 IU kg−1 phytase and 2%, 1.5%, 1%, 0.5%, 0% concentrations of NaH2PO4. Thus, dietary NaH2PO4 was substituted with phytase at ratios of 0%, 25%, 50%, 75% and 100% respectively. Triplicate tanks were each filled with 50 juvenile fish (3.5 ± 0.1 g), which were fed one of the seven experimental diets. Substituting phytase for NaH2PO4 didn't diminish the growth performance, protein, dry matter, lipid and ash deposit and protein retention in the whole body and reduced feed conversion ratio compared to the reference diet. Moreover, phytase substitution at level of 0–50% enhanced P, Mg and Ca deposit. However, weigh gain had a tendendy of decreasing with increasing substituted level. Phytase substituted level exceeding 75% decreased serum P concentration compared to the control group. Apparent digestibility of P peaked when 1000 IU kg−1 phytase substituted 50% NaH2PO4. Phytase also increased apparent digestibility of protein. The improvement of digestibility of protein and P resulted in the decrease in N load by 25% and P load by 31% to environment. Therefore, 50% dietary NaH2PO4 can be substituted by 1000 IU kg−1 feed phytase for juvenile yellow catfish.