Abstract
Background:
Formalin is a widely used chemical with toxic effects on various organs. Its exposure may harm reproductive organs, especially in quails, which are sensitive models for toxicological research.

Aim:
This study aimed to investigate the effects of 5% formalin gas exposure on quail testicular health, blood parameters, hormone levels, and tumor protein TP53 (TP53) gene expression.

Methods:
Twenty male Japanese quails were randomly divided into four groups. The control group received no exposure. The remaining three groups were exposed to 5% formalin gas twice daily for 2 hours over 10, 20, and 30 days. Blood and testicular samples were collected at each time point. Testosterone levels, complete blood count, histopathology, and real-time quantitative polymerase chain reaction (RT-qPCR) for TP53 expression were analyzed. Data were evaluated using one-way analysis of variance (p ≤ 0.05).

Results:
Exposed quails exhibited anxiety, weight loss, and respiratory distress. Body weight decreased progressively from 200 ± 0.66 g (control) to 130 ± 0.43 g (30-day group). The testicular weight increased from 2.12 ± 0.25 g (control) to 4.45 ± 0.34 g (30-day group), with significant enlargement (p < 0.05). Testosterone dropped from 2.22 ± 0.30 ng/ml (control) to 0.9 ± 0.07 ng/ml (30-day group), showing a time-dependent decline (p < 0.05). wWhite blood cells, red blood cells, and hemoglobin (HGB) levels increased significantly, whereas lymphocytes decreased (p <0.05). Histology revealed seminiferous tubule damage and necrosis. RT-qPCR revealed upregulated TP53 expression, especially in the 30-day group (p = 0.018).

Conclusion:
Formalin gas exposure harms quail testes by reducing hormones, altering blood counts, damaging tissues, and increasing TP53 gene expression. This suggests the potential testicular toxicity and carcinogenic risk of formalin.

Key words: Formalin; Gene expression TP53; Quail; Testes.