BACKGROUND: Ca and P intake during brooding affects laying hens' later production and health, with availability varying among strains, necessitating further investigation of the factors influencing these differences. OBJECTIVES: This study aimed to compare the availability of Ca and P and related gene expression among three high-yielding layer strains during the first 6 weeks and identify genes strongly associated with nutrient absorption. METHODS: Ninety pullets (1-d-old, female) from three strains (ML, LM and DS weighted 31.533±0.63g, 39.367±1.40g and 34.099±0.64g, respectively) were randomly assigned to six replicates of fifteen birds each for 6 week cage rearing. Feces were collected weekly to track the Ca and P availability. Initial and final body weights and tibial lengths were recorded to determine growth performance. Intestinal samples were collected to determine the gene expression of Ca and P transporters (TRPV6, CaBP-D28k, NCX1, PMCA1b, NPt2b) as well as tight junction proteins (CLDN-2, CLDN-12). RESULTS: ML and LM pullets exhibited significantly greater body weight (443g, 436g vs 319g, P <
0.001) and tibial length (70.6mm, 69.6mm vs 59.2mm, P <
0.001) than DS. Notably, during the 6 CONCLUSIONS: The study indicated that expression of Ca and P transporter is highest in the duodenum, and duodenal NCX1, NPt2b were the genes most significantly positively correlated with the retention and excretion of Ca and P in pullets.