Replacement of zinc sulphate by microbial phytase for piglets given a maize-soya-bean meal diet

Forty-eight pigs, weaned at 27 days of age at an average body weight of 7.55 kg were used in a 19-day experiment to investigate the influence of microbial phytase on zinc utilization and to calculate equivalency values of zinc as sulphate for microbial phytase. Eight experimental diets were formulated : a maize-soya-bean meal basal diet containing 30 mg of zinc per kg supplemented with 10, 25, 40 or 100 mg of zinc from sulphate ( ZnSO4, 7H(2)O) per kg or with 100, 250, 500 or 750 units ( U) of microbial phytase (3-phytase from Aspergillus niger, Natuphos (R)) per kg. The dietary supplies of calcium and phosphorus were adjusted accounting for the release of these elements by microbial phytase. The copper concentration in the diets was 11 mg/kg. Pigs were given the basal diet for a 7-day adjustment period prior to the 19-day experimental period. At the end of the experiment, bone ash, phosphorus and calcium concentrations as well as plasma and liver copper concentrations were independent of the diet ( P > 0.10). The zinc status of piglets was assessed through plasma alkaline phosphatase activity ( APA) and zinc concentration, bone zinc concentration and liver zinc concentration. Plasma zinc, plasma APA and bone zinc increased linearly (P < 0.001) and quadratically ( P < 0.01, P < 0.001 and P < 0.001, respectively) with zinc added. These parameters also increased linearly (P < 0.001) and quadratically ( P < 0.05, P < 0.001 and P < 0.05, respectively) with phytase added. Liver zinc increased quadratically ( P < 0.05) with zinc added and tended to increase linearly with phytase added ( P = 0.077). Linear and non-linear response equations of indicators of zinc status to zinc added and phytase added were developed and used to calculate zinc equivalency values of phytase. Non-linear models were linear plateau models for zinc added and exponential models for phytase added. Plasma APA, plasma zinc and bone zinc were maximized when zinc added reached 43, 54 and 56 mg/kg of diet, respectively. The mean function of equivalency of zinc as sulphate ( Zn, mg/kg of diet) for microbial phytase ( Phyt, U per kg of diet) was Zn = 49.9-58 .3 e(-0.00233 Phyt). From this equation it is calculated that 250, 500, and 750 U of 3-phytase from Aspergillus niger can avoid the addition of 17, 32 and 40 mg of zinc as sulphate in a piglet diet. Zinc ingested and, in turn, zinc excreted, may be proportionately reduced by almost 0.30 by replacing 30 mg of zinc as sulphate by 500 U of phytase as Natuphos (R) in a piglet maize and soya-bean meal diet formulated to contain 100 mg of zinc per kg.