Background: Heat stress during summer impairs reproductive performance in sows, causing summer infertility. Cytochrome P450 1A2 (CYP1A2) plays a crucial role in steroid hormone metabolism in the liver and has been shown to be upregulated under stress conditions. However, the effect of seasonal heat stress on CYP1A2 expression in sow ovaries remains poorly understood. Methods: Ovaries were collected from crossbred sows during different seasons in Korea. The control group (CON) was exposed to optimal temperatures for swine rearing (22.0-24.5℃) during spring, while the heat-stressed group (HS) experienced high temperatures (30.5-37.0℃) during summer. Temperature-humidity index (THI) was calculated to assess thermal stress severity. CYP1A2 expression was analyzed using Western blotting and immunohistochemistry (IHC), and these values were statistically compared with THI by Pearson’s correlation analysis. Results: The HS exhibited significantly higher THI values compared to the CON (88.11 vs. 66.67). Western blot analysis revealed significant upregulation of CYP1A2 expression in the HS compared to CON (1.89 vs. 1.00). IHC demonstrated that CYP1A2 was specifically localized in granulosa cells of mature follicles, with a significantly higher proportion of CYP1A2-positive follicles in the HS (15.92%) compared to CON (9.08%). When the obtained values were compared with THI values, CYP1A2 expression showed a strong positive correlation with THI (r = 0.41 and 0.74). Conclusions: This study revealed that heat stress can alter the ovarian microenvironment, including the expression of CYP1A2. These findings emphasize the need for effective thermal management strategies to mitigate heat stress-induced reproductive dysfunction in livestock production.

ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
    Ethics statement
    Animals and sampling
    Temperature-humidity index (THI) calculation andstress thresholds
    Western blotting for quantitative expression ofCYP1A2
    Immunohistochemistry (IHC) for detection CYP1A2 inovarian tissue
    Statistical analysis
RESULTS
    THI values and heat stress severity in differentseasons
    CYP1A2 expression in the ovaries of sows in differentseasons
    Immunohistochemistry of CYP1A2 in the ovaries ofsows in different seasons
DISCUSSION
CONCLUSION
SUPPLEMENTARY MATERIALS
REFERENCES

• Young-Bum Son(College of Veterinary Medicine, Chonnam National University, Gwangju 61186, Korea)
• Seong-Eun Heo(Gyeongsangbuk-Do Livestock Research Institute, Yeongju 36052, Korea)
• Do-Yoon Kim(Gyeongsangbuk-Do Livestock Research Institute, Yeongju 36052, Korea)
• Tae-Gyun Kim(College of Veterinary Medicine, Kyungpook National University, Daegu 41566, Korea)
• Hyun-Seung Lee(College of Veterinary Medicine, Kyungpook National University, Daegu 41566, Korea)
• Sung-Ho Kim(College of Veterinary Medicine, Kyungpook National University, Daegu 41566, Korea)
• Seung-Joon Kim(College of Veterinary Medicine, Kyungpook National University, Daegu 41566, Korea)
• Won-Jae Lee(College of Veterinary Medicine, Kyungpook National University, Daegu 41566, Korea, Institute for Veterinary Biomedical Science, Kyungpook Natitonal University, Daegu 41566, Korea) Corresponding author