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Context Thermal stress causes significant changes in the bioavailability of minerals, especially calcium, in laying birds, resulting in reduced egg production, and compromising egg quality. Therefore, it is necessary to use additives that provide better nutrient availability and minimise the negative effects caused by high temperatures. Aims This study aimed to evaluate the effects of super-dosing the diet of laying quails submitted to different temperatures with phytase on their bone parameters and on the epithelial calcium transporter calbindin-D28K positivity. Methods Seven hundred and twenty (720) Japanese quails in the production phase were distributed in a completely randomised design, in a 5 × 3 factorial design, with five supplementation levels of phytase (0, 500, 1000, 1500, and 3000 FTU/kg), and three temperatures (24°C, 30°C and 36°C), totalling 15 treatments, and six replications of eight birds each. The study began at the 8th week of age and continued for two cycles of 21 days, totalling 42 days of experiment. Bone parameters of the tibias and calbindin-D28K positivity were measured by immunohistochemistry. The data were submitted to variance, Tukey, and regression analyses. Key results At 24°C, birds had higher averages for proximal, medial, and distal diaphyses than did birds at 30°C and 36°C, and a greater breaking strength of the tibias than did those at 36°C. There was an increasing linear effect on the medial diaphysis and Seedor index in the tibias with an increasing phytase supplementation level. Calcium (Ca) in the tibias was higher in birds kept at 30°C at a supplementation level of up to 1000 FTU of phytase, than in the birds at 24°C and 36°C, equalling at 1500 FTU, and lower at 3000 FTU. There was a quadratic effect for phosphorus (P) and the Ca:P ratio in the tibias of quails submitted to increasing concentrations of phytase. Quails kept at 30°C showed greater anti-calbindin-D28K positivity in the duodenum and jejunum, when compared to animals subjected to temperatures of 24°C and 36°C. Phytase doses of 500 and 1000 FTU increased calbindin-D28K positivity in the duodenum of quails kept at 30°C. At a supplementation level of 1500 FTU, phytase provided greater eggshell thickness and greater calbindin-D28K positivity in the uterus of quails kept at 36°C. Conclusions Therefore, it is recommended to use 1500 FTU of phytase for Japanese quail exposed to high temperatures. Implications These findings suggest that dietary phytase super-dosing can help alleviate thermal stress in Japanese quail.
Ribeiro et al. (Mon,) studied this question.