Comparative evaluation of the efficacy of cereal and microbial phytases in growing pigs fed diets with marginal phosphorus supply

Two experiments with a total of 76 growing pigs (average initial body weight 16.6 kg) were conducted to compare the efficacy of cereal phytases (wheat and rye) and supplemented microbial phytase (Natuphosl(R)). Using the slope ratio technique, the dose-response relationship between five levels of phytase (0, 50, 100, 150 and 200 Ukg(-1)) and the apparent absorption of phosphorus (P) within each source of phytase was calculated. Graded phytase levels in the diets were obtained by adding increasing amounts of microbial phytase or phytase-containing wheat (Exp 1) or rye (Exp 2) to phytase-inactivated basal diets at the expense of phytase-inactivated wheat (Exp 1) or rye (Exp 2). Except for wheat phytase, addition of phytase to the basal diets increased (P < 0.05) apparent P absorption, with microbial phytase being more efficient (P < 0.05) than cereal phytase. There were no significant differences in apparent P absorption between the wheat- or rye-based diets when either microbial or cereal phytases were supplemented from 0 to 200Ukg(-1). It could be derived from the results of this study, by means of regression analysis, that the efficacy of cereal phytases was 40% compared to microbial phytase. (C) 2002 Society of Chemical Industry.