Effects of dietary phytase and cholecalciferol on phosphorus bioavailability in rainbow trout (Oncorhynchus mykiss)

A study was conducted to examine the influence of dietary inclusion of phytase and high levels of cholecalciferol on phytate phosphorus (P) utilization of rainbow trout. Triplicate groups of rainbow trout, initial weight 51.6 g, were fed in excess diets containing 0 or 1500 units phytase kg(-1) and 2500, 250,000 or 2,500,000 IU cholecalciferol kg(-1) for 12 weeks. The basal diet provided 5.8 and 3.2 g total and phytate P kg(-1) dry matter, of which most was derived from soy protein concentrate. Weight gain of fish was increased by phytase supplementation but decreased by higher cholecalciferol concentrations. Inclusion of phytase improved P availability as indicated by significantly higher apparent availability of P and bone ash and plasma and body P concentrations. Dietary cholecalciferol content did not influence P utilization. An increase in dietary cholecalciferol concentration caused higher deposition of calcium, magnesium and zinc in the kidney. Both cholecalciferol and phytase supplementation significantly (P < 0.05) increased the hepatic cholecalciferol concentration. In summary, dietary phytase supplementation was effective in reducing P load of rainbow trout fed soybean protein concentrate-based diet. High levels of cholecalciferol (250,000 and 2,500,000) had no beneficial effect on P utilization. (C) 1998 Elsevier Science B.V. All rights reserved.