Weaning is challenging for dairy calves, frequently resulting in digestive issues. This highlights the importance of implementing appropriate nutritional strategies to enhance gut health and support optimal growth. Postbiotics is a promising alternative to traditional probiotics, conferring health benefits without the risks associated with live bacteria. This study aimed to investigate the effect of dietary supplementation with a postbiotic from dead-cell C37 (postbiotic LIC37) on blood biochemical parameters and jejunal epithelium transcriptomic profiles in calves. Fourteen Holstein bull calves were randomly allocated into two groups (n = 7). The control group (CON) received a basic diet, while the postbiotic group (DCLI) was supplemented with 1 g/d of postbiotic LIC37 for 90 days. Blood samples were collected on days 76, 83, and 90, respectively. The jejunal epithelial tissue was obtained from four randomly selected calves per group at day 90 for transcriptome analysis. The results showed that postbiotic LIC37 supplementation reduced globulin, total protein, neutrophil (Neu) levels, and neutrophil-to-lymphocyte ratio (NLR) levels in the DCLI group ( < 0.05). Transcriptomic analysis identified 76 differentially expressed genes (DEGs), with significant upregulation of genes involved in fatty acid metabolism (FABP1), intestinal barrier function (B4GALNT2), and detoxification (GSTA1), alongside downregulation of immune response regulation (FCRLA, FCRL4). Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses highlighted enrichment in pathways related to glutathione metabolism, drug metabolism, and vitamin digestion, indicating that postbiotic supplementation improved detoxification, oxidative stress defense, and nutrient absorption in calves. This study provides novel insights into the molecular mechanisms underlying the benefits of postbiotic LIC37 and supports its potential as a sustainable alternative to probiotics in calf nutrition.