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.