effect of phytase superdoses and citric acid on growth performance, plasma phosphorus and tibia ash in broilers fed canola meal-based diets severely limited in available phosphorus

this experiment was conducted to investigate the effect of phytase superdoses alone or in combination with citric acid (ca) in canola meal-based diets severely limited in available phosphorus (pa) on growth performance, plasma phosphorus (p), and tibia ash (ta) in broilers from 22 to 42 d of age. two hundreds and eighty 21-d-old male broilers were used in 28 pens of 10 birds per each. the experimental diets consisted of a positive control (pc) diet and six negative control (nc) diets which consisted of two levels of ca (0 and 20 g/kg) and three levels of phytase (0, 1000 and 4000 u/kg) in a 2 × 3 factorial arrangement. the pc diet contained 4.3 g/kg pa, but all nc diets contained 1.5 g/kg pa. results indicated that the birds fed the pc diet had a significantly higher average daily gain (adg), plasma p and ta, but a lower feed conversion ratio (fcr) than those fed the nc diet. the adg, fcr and plasma p values in birds fed nc diets supplemented with 4000 u/kg phytase enzyme (with or without ca) significantly reached those of birds fed the pc diet. but, addition of phytase enzyme at 1000 u/kg only plus ca to the nc diet could significantly improve fcr and plasma p. a significant interaction was observed between phytase and ca for fcr and plasma p. although ta values in nc + 1000 u/kg phytase treatments (with or without ca) were similar to the pc treatment, ta values of nc + 4000 u/kg phytase treatments (with or without ca) was greater than that of the pc treatment. results of this study showed that, in severely limited pa corn-canola meal-based diets, supplementing 4000 u/kg phytase or also 1000 u/kg phytase plus ca will be sufficient to obtain the comparable feed efficiency in broilers to those fed the adequate pa diet.