Photoperiodic and hormonal influences on fur density and regrowth in two hamster species

Matthew J. Paul, Nicole T. George, Irving Zucker, Matthew P. Butler

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


Temperate and boreal mammals undergo seasonal changes in pelage that facilitate thermoregulation in winter and summer. We investigated photoperiodic influences on pelage characteristics of male Siberian and Syrian hamsters. Fur density (mg fur/cm2 skin) was measured by weighing the shavings of fur patches removed from the dorsal and ventral surfaces of hamsters maintained in long days (LDs) or transferred to short days (SDs). Patches were reshaved 3 wk later to assess fur regrowth (mg regrown fur/cm2 skin). Fur density was greater in SD than in LD Siberian hamsters after 11 wk of differential phototreatment. The onset of increased fur density in SDs was accompanied by a transient increase in fur regrowth (11-14 wk on the dorsal surface and 7-10 and 11-14 wk on the ventral surface), suggestive of a seasonal molting process. Fur density, body mass, and pelage color of Siberian hamsters returned to values characteristic of LD males after a similar duration of prolonged (>27 wk) SD treatment and appear to be regulated by a similar or common interval-timing mechanism. In Syrian hamsters, dorsal fur density, fur regrowth, and hair lengths were greater in SD than in LD males. Castration increased and testosterone (T) treatment decreased dorsal and ventral fur regrowth in LD and SD hamsters, but the effects of T manipulations on fur density were limited to a decrease in dorsal fur density after T treatment. Decreased circulating T in SDs likely contributes to the seasonal molt of male hamsters by increasing the rate of fur growth during the transition to the winter pelage.

Original languageEnglish (US)
Pages (from-to)R2363-R2369
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Issue number6
StatePublished - Dec 2007
Externally publishedYes


  • Photoperiodism
  • Siberian hamster
  • Syrian hamster
  • Testosterone

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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