IntroductionThe eastern massasauga rattlesnake (Sistrurus catenatus) is a pygmy rattlesnake at risk of extinction in North America. Conservation breeding and reintroduction efforts have been established by the Association of Zoos and Aquariums (AZA) to safeguard the species, but a comprehensive mortality study has not yet been completed that could lead to enhanced conservation efforts from better informed management. A common health issue noted for rattlesnakes under managed care is spinal lesions, often associated with Salmonella infections. The cause and factors affecting this disease are unknown, and the exact prevalence over time and across institutions is underexplored.MethodsA retrospective mortality study with targeted analysis of spinal lesions for 273 eastern massasaugas (153 deceased and 120 alive) was completed using medical records shared from 18 AZA institutions spanning 1989-2025.ResultsThe most prevalent causes of death overall were sepsis/septicemia (n=23), spinal lesion/osteomyelitis (n=17), and cancer/neoplastic process (n=14). The most common comorbidity overall was female reproductive disease (n=40). The average age of death was 65 ± 5 months (5.4 years). Statistical modeling revealed that Salmonella enterica subsp. arizonae presence, sex (female), and age (older) were predictors of spinal lesions.DiscussionOur results suggest that S. enterica subsp. arizonae is a potential model of spinal lesion pathogenesis, and increased surveillance of serovars (e.g. IIIa:56:z4,z23:-) should be established. The results from this study can be used by practitioners to make more informed management decisions for massasauga rattlesnakes in conservation breeding and reintroduction programs to improve the health of animals in this understudied taxon, ultimately improving conservation impact.