The effect of citric acid and microbial phytase on mineral utilization in broiler chicks

An experiment was conducted to study the effect of microbial phytase (Natuphos((R)) 500) supplementation in chicks fed different levels of available phosphorus (AP) and citric acid (CA) on performance, mineral retention (Ca, P, Mg, and Zn), bone and plasma minerals (Ca, P, Mg, and Zn), plasma total protein (TP), and serum aspartate ammotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH) activities. Data were analyzed as a 2 x 4 x 2 factorial arrangement with two levels of AP (3.5 and 2.5 g/kg), four levels of phytase (0, 200, 400 and 600 U/kg), and two levels of citric acid (0 and 20 g/kg). The low-AP diets reduced performance. Phytase supplementation increased weight gain (up to 7% quadratically) and feed consumption (up to 5 %). This response was statistically maximized by 200 U/kg phytase. Feed to gain ratio was not affected by phytase addition. Growth response to phytase was negatively affected by citric acid. Decreasing AP content in the diet increased Ca, P, and Mg retention, and reduced Zn retention. Phytase supplementation linearly increased Ca, P, and Zn retention by 9, 10 and 16%, respectively. Citric acid addition also increased Ca, P, and Zn retention by 3, 3 and 4%, respectively. Likewise, the decrease in AP content in the diet caused a reduction of tibia ash and tibia Zn, and an increase in tibia Ca and P contents. Phytase supplementation increased tibia ash (up to 4%), tibia Ca (up to 2%), P (up to 1%) and Zn (up to 4%) contents, tibia weight (up to 9%), and relative tibia (up to 19%) and liver (up to 13%) weights. Citric acid increased tibia ash (2%), and tibia Ca (2%) and P (2%) contents. Finally, by decreasing AP levels in the diet, plasma Ca and Zn concentrations as well as AST, ALP, and LDH activities were increased. However, plasma P and TP content were reduced. Phytase supplementation increased linearly plasma Ca (up to 4%), P (up to 12%), Mg (up to 10%), Zn (up to 22%) and TP (up to 7%) content, and serum AST (up to 22%), ALT (up to 40%), and LDH (up to 17%) activities, and reduced linearly serum ALP (up to 34%) activity. Citric 1014, and 5%, respectively, and reduced ALP activity by 13%. In conclusion, these results indicated that the addition of phytase to maize and soyabean meal low-AP diets improved the performance and increased Ca, P, and Zn utilization in chicks. However, the inclusion of citric acid depressed the performance and caused an increase in mineral utilization. Growth response to phytase was negatively affected by citric acid. (C) 2003 Elsevier B.V. All rights reserved.