Effects of exogenous phytase supplementation on the modulation of hormonal responses in Japanese quails (Coturnix japonica) at high environmental temperatures during the production phase

This study investigated the endocrine-modulatory effects of dietary phytase supplementation in laying Japanese quails (Coturnix japonica) exposed to thermal stress. A larger batch of quails was reared from the first day of life under controlled environmental conditions. At 56 days of age (8 weeks), 720 quails with uniform zootechnical characteristics were selected and allocated to five dietary treatments (0, 500, 1,000, 1,500 and 3,000 FTU/kg) and three thermal conditions: thermal comfort (24°C) and heat stress (30°C and 36°C). Each treatment included six replicates with eight quails per experimental unit. The experiment lasted 105 days, divided into three production periods. Serum concentrations of corticosterone, triiodothyronine (T3) and thyroxine (T4) were measured. The use of phytase overdoses (1,500 and 3,000 FTU/kg) significantly increased the concentration of corticosterone in a severe heat stress environment (36°C) during the peak of laying but reduced in the final phase of evaluation. At the beginning of production, T3 levels increased under moderate heat stress (30°C) with phytase from 1,000 FTU/kg, while in severe heat stress the levels increased from 1,500 FTU/kg. A similar effect was observed in T4 concentrations. Although phytase overdosing intensified stress responses at peak laying, it exerted a positive modulatory effect during later stages, highlighting its potential to support endocrine adaptation under high temperatures.