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Biology of Reproduction 63, 179-187 (2000)
© 2000 Society for the Study of Reproduction, Inc.

Regular article

Age-Dependent Changes in Sperm Production, Semen Quality, and Testicular Volume in the Black-Footed Ferret (Mustela nigripes)1

K.N. Wolfa,b, D.E. Wildta, A. Vargasb, P.E. Marinarib, J.S. Kreegerb, M.A. Ottingerc, and J.G. Howard2,a

a Conservation & Research Center, National Zoological Park, Smithsonian Institution, Front Royal, Virginia 22630 b National Black-Footed Ferret Conservation Center, United States Fish & Wildlife Service, Laramie, Wyoming 82070 c University of Maryland, College Park, Maryland 20742

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.

FOOTNOTES

First decision: 20 December 1999.

1 Supported in part by the Phoenix Zoo, the U.S. Fish & Wildlife Service, Missy and Clint Kelly, and the Conservation & Research Center's NOAHS NETWORK. This work was in partial fulfillment of a Masters of Science degree by the senior author (K.N.W.).

2 Correspondence: JoGayle Howard, Reproductive Physiology Program, National Zoological Park, Smithsonian Institution, Washington, DC 20008. FAX: 202 673 4733; jhoward{at}nzp.si.edu






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