Influence of pregnancy on the mammary gland of Kazakh horses based on whole-transcriptome sequencing

Kazakh mares have drawn significant attention for their outstanding lactation traits. Lactation, a complex physiological activity, is modulated by multiple factors. This study utilized high-throughput sequencing to conduct whole-transcriptome sequencing analysis on the mammary gland tissue of 8 Kazakh mares, of which 4 were pregnant and 4 were non-pregnant, to systematically reveal the molecular regulatory mechanisms. The results showed differential expression in 2,136 mRNAs, including PIK3CG, CLEC4E, and UBDH1-5; 180 lncRNAs, including MSTRG.2989.2, MSTRG.11654.1, and MSTRG.13688.1; 104 miRNAs, including eca-miR-146a, eca-miR-21, and miR-375-y; and 1,162 circRNAs such as novel_circ_025824, novel_circ_031697, and novel_circ_021617. Gene Ontology functional annotation indicates that these differentially expressed genes are involved in multiple key biological processes, such as the cellular process (BP), metabolic process, and biological regulation. Kyoto Encyclopedia of Genes and Genomes analysis suggests that the differentially expressed genes are significantly enriched in essential pathways such as cytokine-cytokine receptor interaction, the chemokine signaling pathway, and the PI3K-Akt signaling pathway. This study compared genomic differences in mammary gland tissue of pregnant and non-pregnant Kazakh mares and identified candidate genes that are closely related to lactation regulation. It found that various genes, such as PIK3CG, IL7R, and SOD2, play central regulatory roles in activating mammary gland functions. These findings provide theoretical support for explaining the molecular mechanisms underlying the mammary gland development of Kazakh horses.