Effects of chronic mild heat stress on reproductive performance, ovarian development, and HPO axis hormone secretion in broiler breeders.

Heat stress poses a major challenge in poultry production, yet little is known about its chronic effects in broiler breeders. In this study, 144 broiler breeders were exposed to 32°C of chronic heat stress, and effects on egg production, physiological parameters and reproductive hormones, organ weights, and follicle counts were evaluated. The results showed that the heat stress significantly reduced egg production, average egg weight, uterus weight, small yellow follicle (SYF) and large white follicle (LWF) counts; and also reduced serum triiodothyronine (T3), serum total cholesterol (TC), and increased liver triglycerides (TG). Moreover, hypothalamic and serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol (E2) levels were suppressed. These results suggest that mild chronic maternal heat stress impairs reproductive performance through an integrated mechanism involving, metabolic adjustments, hypothalamic-pituitary-ovarian (HPO) axis suppression, and impaired follicular and hepatic function. This study provides a mechanistic basis for understanding heat-induced reproductive impairment and its potential impact on offspring.