Fasting-induced physiological remodeling alleviated fatty liver in laying hens through regulating hepatic lipid metabolism

Aging laying hens in the late production phase are prone to fatty liver syndrome due to dysregulated lipid metabolism. Although fasting has been shown to reduce hepatic lipid accumulation in mammals, its mechanistic effects in poultry remain unclear. This study investigated whether fasting-induced physiological remodeling alleviates fatty liver in late-phase laying hens and explored the underlying molecular mechanisms. Fasting significantly reduced liver size, liver index, and hepatic triglyceride content (p < 0.05), accompanied by decreased Oil Red O staining, indicating attenuated lipid deposition. Serum estradiol (E2) concentrations decreased during fasting, whereas triiodothyronine (T3) and thyroxine (T4) concentrations increased and returned to baseline following refeeding (p < 0.05). Fasting induced transient oxidative stress, evidenced by elevated MDA levels, whereas hepatic GSH-Px activity and the mRNA expression of SOD, CAT, and GSH-Px increased during the recovery phase, indicating enhanced antioxidant capacity (p < 0.05). Liver function markers (ALT and AST) increased in serum but decreased in liver tissue during fasting, returning to normal levels after refeeding, thereby reflecting a reversible adaptive response (p < 0.05). Transcriptome and qPCR analyses revealed that autophagy-related genes (PIK3CB, ERN1) were upregulated during fasting, whereas pro-apoptotic genes (CASP-3, CASP-7) were downregulated, and the anti-apoptotic gene BCL2 was elevated (p < 0.05), indicating that fasting activated autophagy while suppressing apoptotic signaling, thereby potentially promoting hepatocellular survival during metabolic stress. The expression of the lipid synthesis gene ACAT2 decreased, while the decomposition gene ACSL1 increased (p < 0.05). Western Blot further confirmed enhanced expression of key autophagy proteins (PI3K, Beclin1, LC3) and suppression of mTOR, demonstrating that lipids were partially degraded via the autophagy pathway to supply energy. In conclusion, fasting-induced physiological remodeling effectively alleviated fatty liver in late-phase laying hens. This study provides mechanistic insight into nutritional regulation of hepatic lipid homeostasis and offers a theoretical basis for extending the laying cycle in commercial production.