Emerging evidence proposes that the gut microbiome has an vital role in host growth, metabolism and endocrinology. That is, gut microbes impact growth by potentially altering the growth hormone (GH)/insulin-like growth factor-1 axis. Our previous research has also shown that GH - in states of absence and excess - is associated with altered gut microbial composition, maturity and predictive metabolic function in mice. Moreover, both GH and the gut microbiome are implicated in development and aging. Yet, it is unknown how GH impacts the longitudinal microbiome. This study thus aimed to characterize the longitudinal changes in the gut microbial profile of bovine GH transgenic mice (a model of chronic, excess GH action and accelerated aging). Microbial composition was quantified from fecal pellets of the same bGH and control mice at 3, 6 and 12 months of age through 16S rRNA gene sequencing and QIIME 2. Additional bioinformatic analyses assessed the unique signature and predictive metabolic function of the microbiome. The bGH mice had a distinct microbial profile compared to controls longitudinally. At 3 months, bGH mice had increased Firmicutes and Actinobacteria, decreased Bacteroidetes, Proteobacteria and Campylobacterota, and a significant reduction in microbial richness and evenness. By 6 months, all of the aforesaid phyla were increased with the exception of Firmicutes. By 12 months, bGH mice exhibited dysbiosis with increased Firmicutes and Proteobacteria and reduced Bacteroidetes, microbial richness and evenness. Moreover, abundance in Firmicutes, Bacteroidetes and Campylobacterota were significantly explained by the combined effect of genotype and age (p = 0.006, 0.005 and 0.02, respectively). Across all timepoints, bGH mice had a significantly different microbiome compared to controls (p = 0.002), and the development of microbial richness and evenness were also significantly different in bGH mice (p = 0.034 and 0.023). Bacterial genera Lactobacillus, Ruminococcaceae and Lachnospiraceae were identified as a unique candidates in bGH mice across all timepoints. Likewise, metabolic pathways involved in biosynthesis of heme b, menaquinol, acetate and butyrate differentiated the longitudinal bGH microbiome. Collectively, these results show that chronic, excess GH impacts the development and aging of the gut microbiome. Notably, several of the stated bacterial genera and metabolic pathways were associated with GH in our previous study, suggesting that GH may influence the longitudinal presence of certain gut microbes and metabolic functions. Additional studies will be performed to further explore the GH-associated gut microbiome and its impact on host health. Research was partially funded by the John J. Kopchick MCB/TBS Fellowship, a fellowship from the Osteopathic Heritage Foundation and the MMPC at UC, Davis (NIH grant U240DK092993).