Comparative study on calcium and phosphorus metabolism and transcriptomic analysis in laying hens producing translucent and sand-shelled eggs

Based on previously observed eggshell defects of translucent eggs and sand-shelled eggs, this study systematically elucidates their formation mechanisms and key physiological differences in laying hens through multi-omics approaches. Sand-shelled eggs were characterized by altered serum calcium-regulating hormones profiles, lower tibial strength, downregulated uterine calcium-phosphorus transport genes, and impaired mammillary layer formation. Translucent eggs exhibited distinct phenotypic traits, including significantly fewer eggshell pores and greater shell weight, along with markedly downregulated uterine calcium-phosphorus transport genes and compensatory upregulation of the corresponding genes in the duodenum and kidney. Transcriptomic analysis further revealed that PPAR signaling and peroxisome pathways were activated in the duodenum of hens laying translucent eggs, with heat shock protein HSPH1 consistently upregulated across three tissues, indicating energy-lipid metabolic reprogramming and modest cellular stress. In conclusion, the formation of translucent eggs primarily resulted from localized uterine calcium-phosphorus secretion dysfunction and its consequent systemic metabolic adaptation and stress response, whereas sand-shelled eggs resulted from systemic calcium deficiency and more severe uterine functional impairment. This study provides novel insights into the regulatory network of eggshell biomineralization and offers a theoretical basis for improving eggshell quality.