This study aimed to evaluate the effects of phytase superdosing in the diet of Japanese quails subjected to different thermal conditions on productive performance, egg characteristics, intestinal morphometry, and physiological parameters. The experiment was conducted in a completely randomized design in a 5 × 3 factorial arrangement, consisting of five phytase levels (0, 500, 1000, 1500, and 3000 FTU/kg) and three temperatures (24, 30, and 36°C), with six replicates of eight birds each. The performance variables evaluated included feed intake, egg production, egg weight, egg mass, feed conversion per egg mass, and feed conversion per dozen eggs. Egg quality was assessed by yolk color, shell thickness, specific gravity, Haugh units, and proportions of yolk, albumen, and shell. Spleen, liver, heart, and abdominal fat weights were also measured, along with duodenum and jejunum morphometry. Data were subjected to analysis of variance, Tukey's test, and regression analysis. Birds kept at 36°C showed lower feed intake compared with those maintained at 24 and 30°C (P < 0.001), with no significant effect of phytase on performance. Supplementation with 1500 FTU increased eggshell thickness at 36°C (P < 0.001). A temperature × phytase interaction was observed for liver weight (p = 0.010), whereas heart weight was higher at 24°C compared with 36°C (P = 0.005). The effects of phytase on duodenal morphometry were temperature-dependent, with the greatest absorptive area observed with 3000 FTU at 30°C (P < 0.001). The temperature of 24°C resulted in the best morphological parameters and the lowest hepatic glycogen index. It is concluded that although quails tolerate temperatures of 36°C, the best productive responses occur at 30°C. Therefore, the use of 1000 to 1500 FTU is recommended, as these levels provided benefits to intestinal morphometry and egg quality.
Keywords: Egg quality; Heat stress; Intestinal morphology; Japanese quail; Phytase superdosing.
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