title: Age-dependent changes in sperm production, semen quality, and testicular volume in the black-footed ferret (Mustela nigripes).
abstract: The black-footed ferret (Mustela nigripes), which was extirpated from its native North American prairie habitat during the 1980s, is being reintroduced to the wild because of a successful captive-breeding program. To enhance propagation, the reproductive biology of this endangered species is being studied intensively. The typical life span of the black-footed ferret is approximately 7 yr. Female fecundity declines after 3 yr of age, but the influence of age on male reproduction is unknown. In this study, testis volume, seminal traits, sperm morphology, and serum testosterone were compared in 116 males from 1 to 7 yr of age living in captivity. Results demonstrated that testes volume during the peak breeding season was similar (P > 0.05) among 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) structurally normal sperm than younger counterparts; however, serum testosterone concentrations were not reduced (P > 0.05) in older males. Histological comparison of testicular/epididymal tissue from 5- and 7-yr-old black-footed ferrets confirmed that the interval between these two ages may represent a transitional period to reproductive senescence. In summary, functional reproductive capacity of male black-footed ferrets exceeds that of females by at least 2 yr. Testes and seminal quality are indistinguishable among males 1 to 5 yr of age, with progressive reproductive aging occurring thereafter.
authors.affiliation: Conservation & Research Center, National Zoological Park, Smithsonian Institution, Front Royal, Virginia 22630, USA.
authors.forename: K N
authors.initials: KN
authors.lastname: Wolf
authors.forename: D E
authors.initials: DE
authors.lastname: Wildt
authors.forename: A
authors.initials: A
authors.lastname: Vargas
authors.forename: P E
authors.initials: PE
authors.lastname: Marinari
authors.forename: J S
authors.initials: JS
authors.lastname: Kreeger
authors.forename: M A
authors.initials: MA
authors.lastname: Ottinger
authors.forename: J G
authors.initials: JG
authors.lastname: Howard
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D004542:Ejaculation; D004822:Epididymis / Q000033:anatomy & histology / Q000502:physiology; D005289:Ferrets / Q000502:physiology*; D008297:Male; D012661:Semen / Q000502:physiology*; D013081:Sperm Motility; D013094:Spermatozoa / Q000502:physiology*; D013737:Testis / Q000033:anatomy & histology / Q000502:physiology*; D013739:Testosterone / Q000097:blood
chemical_list: D013739:Testosterone