J Anim Physiol Anim Nutr. 2019;1–9. wileyonlinelibrary.com/journal/jpn | 1 © 2019 Blackwell Verlag GmbH Received: 12 August 2018 | Revised: 8 December 2018 | Accepted: 23 January 2019 DOI: 10.1111/jpn.13074 ORIGINAL ARTICLE Combination of phytase and citric acid, but not phytase alone, ensures regular rates of growth and bone mineralization in quails under severe phosphorus restriction Bruno S. Vieira | Joao G. Caramori Junior | Gerusa S. S. Correa | Ines G. Colvara | Emanuele Brusamarelo | Thuani V. S. Pereira | Silvana A. P. V. Barbosa | Cleber F. S. Oliveira College of Veterinary Medicine, Federal University of Mato Grosso, Cuiaba, Brazil Correspondence Bruno S. Vieira, College of Veterinary Medicine, Federal University of Mato Grosso, Cuiaba, Brazil. Email: vieirabs@hotmail.comFunding information CAPES/Brazil, PhD scholarship for the first author. Abstract An experiment was conducted to evaluate the effects of phytase (PHY), alone or in combination with citric acid (CA), on growing Japanese quails under moderate and severe phosphorus (P) restriction. For this, 504 one‐day‐old female quails were dis‐ tributed in a completely randomised design with seven treatments and six replica‐ tions. Treatments consisted of the following diets: (a) positive control (PC): formulated according to quails nutritional requirements; (b) negative control 40% (NC 40 ): PC with 40% less aP; (c) NC 40 +PHY; (d) NC 40 +PHY+CA; (e) negative control 65% (NC 65 ): PC with 65% less aP; (f) NC 65 +PHY; (g) NC 65 +PHY+CA. Phytase and CA were included at 300 FTU/kg and 40 g/kg, respectively. Performance, bone mineralization and plasma mineral concentration were evaluated at day 35; calcium (Ca) and P metabolism, be‐ tween days 36 and 39. No significant differences in performance, plasma Ca and P were detected between quails fed PC or NC 40 ; however, NC 40 decreased tibia ash ( p < 0.01). Treatment NC 65 impaired daily weight gain ( p = 0.01), tibia ash ( p < 0.01), and tibia optical densitometry ( p = 0.03), as well as modified plasma Ca ( p < 0.01) and P ( p = 0.03) concentrations when compared to PC. Both NC 40 and NC 65 reduced P excretion ( p < 0.01). Phytase alone restored tibia ash of NC 40 quails to regular rates. Nevertheless, only PHY and CA combined returned plasma P, tibia ash, tibia optical densitometry, and daily weight gain of quails fed NC 65 to similar values as those ob‐ served in PC. In conclusion, PHY alone suppresses the negative effects of moderate P restriction in growing Japanese quails, but fails in this task under severe P restric‐ tion. In such a situation, only the combination of PHY and CA ensures regular rates of growth and bone mineralization. This concept should be better explored by produc‐ ers in order to take full advantage of the reduction in P excretion achieved by lower‐ ing dietary P concentrations. KEYWORDS bone densitometry, citrate, organic acid, phytase, quail