Anthropogenic destruction of the prairie ecosystem caused the black-footed ferret (ferret; c) to go functionally extinct in the wild in the 1980’s. The last remaining individuals were brought into captivity and a captive breeding program was established, which has genetically managed the population successfully enough to have produced thousands of ferrets since, and has reintroduced ferrets back into the wild. However, the ferret is exhibiting signs of inbreeding depression. Captive fertility rates have steadily declined over the past 30 years. While these declines are tied to increased inbreeding, wild ferrets born in the wild, descendants of captive ferrets, have improved sperm health metrics and anecdotally higher birth rates. This may be a sign of environmental-dependent inbreeding depression (EDID), where something about the captive environment is exacerbating the symptom of infertility. We hypothesize that the captive diet, which contains high levels of vitamin A, is causing oxidative stress in the captive ferrets and thereby worsening the decline in sperm health and ultimately lowering birth rates. At high levels, vitamin A is toxic, pro-oxidative, and antagonistic to antioxidants. We implemented a captive diet study to test whether an antioxidant-supplemented diet (vitamin E) would counteract the negative effects of the vitamin A diet. We also had a cohort of second-generation vitamin E (second-gen) ferrets, born to mothers on the vitamin E diet and fed vitamin E since they were weaned, to test whether positive effects from an antioxidant diet were transgenerational. In Chapter Two, I employed methods to measure sperm DNA damage levels across diets, which are correlated with fertility metrics and found that second-gen ferrets had lower levels of DNA fragmentation. Further, I found that second-gen ferrets had lower levels of total antioxidant capacity, a proxy for the antioxidants in a system, potentially indicating less demand for oxidative repair. In Chapter Three, I measured gene expression in mature sperm across diet treatments and found that wild ferrets had increased functional enrichment in transcripts related to motility and acrosome function, which may be related to their improved sperm metrics. I also found expression of SMARCAD1 gene in vitamin E ferrets, a transcript employed in chromatin repair, that may be related to the improved sperm DNA integrity we observed in second-gen ferrets. In Chapter Four, I focused on utilizing existing reproductive and biographical data collected by captive managers to predict reproductive outcomes using a machine learning pipeline. I found that the most important metrics for predicting birth were sperm metrics, and that past reproductive success in males also positively influenced the ability to predict the outcome. Female factors were not found to be important in predicting reproductive outcomes in these models. Overall, my work shows that while an antioxidant diet can improve fertility metrics, recreating wild conditions in captivity is the surest way to decrease the effects of EDID and improve reproductive success. Additionally, my work shows that several methodologies (sperm transcriptomics and DNA damage) can be successfully employed in non-model endangered species and thereby used to inform science related to the conservation of threatened species.