Does citric acid improve performance and bone mineralization of broilers when combined with phytase? A systematic review and meta-analysis

The aim of this meta-analysis was to critically determine whether citric acid (CA) improves performance and bone mineralization of broilers when used in combination with phytase (PHY) in low-phosphorus diets. A systematic review of the literature was performed electronically on PubMed, Scielo, Science Direct, Scopus, and Web of Science databases; from the total of 574 identified studies, only seven met all the inclusion criteria (3862 broilers). Dietary PHY ranged from 300 to 4000 FTU/kg; CA from 20 to 50 g/kg. Mean differences between PHY+CA and PHY treatments on daily weight gain (DWG), daily feed intake (DFI), feed conversion ratio (FCR), and tibia ash content (TAC) were compared using a random-effects model. Also, subgroup analyses were performed to assess the potential interference of feed and non-feed related characteristics on the overall effect estimates. Chickens fed PHY+CA gained, on average, 2.46 g/day more (P = 0.005) than those fed exclusively with PHY. While no differences on DFI and FCR were detected between treatments, broilers supplemented with PHY+CA increased (P = 0.002) TAC in 3.27%. In general, better performance results for PHY+CA were found on males and broilers receiving PHY up to 500 FTU/kg or CA higher than 20 g/kg. Higher concentrations of phytate phosphorus and calcium also favored the detection of positive effect of PHY+CA on DWG and TAC. Improvement on DWG by PHY+CA was more pronounced in the finishing phase, but TAC responded better to PHY+CA during the starter period. Moreover, treatment period required to detect significant differences between PHY and PHY+CA was larger for DWG than for TAC. No outliers were observed and sensitivity analysis did not modify the overall effect estimates and its associated P value. However, the small number of studies and a possible publication bias in favor of studies with positive effects on FCR might have affected the strength of meta-analysis results. In conclusion, there is evidence that CA improves performance and bone mineralization of broilers when used in combination with PHY, which in individual studies was inconclusive. Moreover, feed and non-feed related characteristics could affect how DWG and TAC respond to PHY and CA.