EFFECT OF AN ADDITION OF MICROBIAL PHYTASE ON ZINC-AVAILABILITY

A study of 35 (5 x 7) male, individually housed, albino rats (initial average weight = 50 g) was undertaken to examine the effect of an addition of microbial phytase to a diet containing phytate on the availability of zinc. The rats were fed a semisynthetic diet based of egg white and cornstarch over a 3-week period. All diets were supplemented with 20 mg Zn/kg. Group I (control) was fed the basal diet free of phytic acid (PA) and phytase. By replacing cornstarch by Na-phytate (0.5 % in group II and 1.0 % group III), molar phytate : Zn ratios of 25 and 50:1 were obtained, respectively. In groups IV (0.5 % PA) and IV (1.0 % PA) 1 000 U of microbial phytase were added. A molar phytate : Zn ratio of 25 (group II) and 50:1 (group III) resulted in a dose-dependent depression of growth and feed efficiency ratio. These negative effects of the addition of PA could be completely counteracted by the supplementation of 1 000 U of phytase in group IV and partially so in group V Similarly, the apparent absorption and retention of Zn, Zn-concentration in femur and testes and different Zn-status-parameters in plasma (Zn-concentration, percent unsaturated plasma-Zn binding capacity, activity of alkaline phosphatase) were improved by adding 1 000 U microbial phytase/kg diet. The present study shows that an addition of microbial phytase to phytate-rich diets considerably improves the availability of Zn in growing rats.