This study evaluated the short-term response of the fecal microbiota of wild Cavia tschudii during its transition from natural conditions to captivity under a standardized alfalfa-based diet. Fecal samples were collected over a 21-day period and analyzed using 16S rRNA gene sequencing to assess microbial diversity, community structure, and taxonomic composition. Rarefaction analysis indicated sufficient sequencing coverage; however, samples were normalized to 500 reads per sample, and results should be interpreted cautiously. No significant changes were detected in alpha diversity, beta diversity, or dominant taxonomic composition across sampling time points. The microbiota was consistently dominated by Bacteroidota and Firmicutes, accounting for more than 85% of total relative abundance. Minor taxa such as Methanobacteriales and Spirochaetales were present at low and stable abundances. Despite differences between natural forage and the alfalfa-based diet, microbial community structure showed limited temporal variation during the study period. The absence of detectable parasitic infections further supports that observed patterns reflect host–microbiota dynamics under controlled conditions. Functional predictions suggested variation in metabolic pathways but should be interpreted cautiously due to the limitations of 16S rRNA-based inference. Overall, these findings suggest limited temporal variation in the fecal microbiota of Cavia tschudii during the first three weeks of captivity under the conditions evaluated. However, due to the exploratory nature of the study and its methodological limitations, these results should be interpreted with caution. This study provides baseline insights into limited temporal variation in the fecal microbiota of a wild caviid species and contributes to understanding host–microbiome interactions relevant to conservation and potential domestication processes.