Age-dependent changes in sperm production, semen quality, and testicular volume in the black-footed ferret (Mustela nigripes)

The black-footed ferret (Mustela nigripes), which was extirpated from its n ative North American prairie habitat during the 1980s, is being reintroduce d to the wild because of a successful captive-breeding program. To enhance propagation, the reproductive biology of this endangered species is being s tudied intensively. The typical life span of the black-footed ferret is app roximately 7 yr. Female fecundity declines after 3 yr of age, but the influ ence of age on male reproduction is unknown. In this study, testis volume, seminal traits, sperm morphology, and serum testosterone were compared in 1 16 males from 1 to 7 yr of age living in captivity. Results demonstrated th at testes volume during the peak breeding season was similar (P > 0.05) amo ng males 1 to 5 yr of age, reduced (P < 0.05) among males 6 yr of age, and further reduced (P < 0.05) among males 7 yr of age. Motile sperm/ejaculate was similar in males 1 to 6 yr of age but diminished (P < 0.05) in those 7 yr of age. Males at 6 and 7 yr of age produced fewer (P < 0.05) structurall y normal sperm than younger counterparts; however, serum testosterone conce ntrations were not reduced (P > 0.05) in older males. Histological comparis on of testicular/epididymal tissue from 5- and 7-yr-old black-footed ferret s confirmed that the interval between these two ages may represent a transi tional period to reproductive senescence. In summary, functional reproducti ve capacity of male black-footed ferrets exceeds that of females by at leas t 2 yr. Testes and seminal quality are indistinguishable among males 1 to 5 yr of age, with progressive reproductive aging occurring thereafter.