Genital abnormalities in white-tailed deer (Odocoileus virginianus) in west-central Montana: pesticide exposure as a possible cause.

From spring, 1996, to early spring, 2000, accident-killed and injured white-tailed deer, Odocoileus virginianus, in the Bitterroot Valley of west-central, Montana, U.S.A., were collected and examined for genital abnormalities at the Bitterroot Wildlife Rehabilitation Center. Of the 254 male deer examined, 133 were fawns aged 3 months to 1 yr, 29 were 1 to 1 1/2 yrs of age, and 92 were 1 1/2 to 3 yrs of age. Approximately 33% were normal; the remaining 67% showed varying degrees of apparent genital developmental anomalies, specifically mispositioned and undersized scrota and ectopic testes, and this percentage held through all age groups. The sex ratio of fawns and fetuses was skewed towards males, significantly so for the 1996 fawn cohort and for the total of all fawns and fetuses in the study. Although possible causes of the genital anomalies, centering on endocrine disrupting pesticides, are discussed, no conclusions of cause and effect can be currently justified.