Western forms of the spotted skunk breed in late September, at which time daylength is decreasing. Early cleavage and tubal transport are normal but implantation is delayed for approximately 220 days and further embryonic development is greatly retarded (Mead, 1968). Corpora lutea involute soon after their formation and progesterone secretion is minimal during embryonic diapause (Mead & Eik-Nes, 1969a). The vulva enlarges in late April, at which time daylength is increasing, progesterone levels increase and embryonic development proceeds rapidly. Nidation is initiated a few days after luteal recrudescence and parturition occurs 29 to 31 days after implantation. These findings suggest that delayed implantation may result from insufficient gonadotrophin secretion during the preimplantation period.
The duration of the preimplantation period of the spotted skunk can be significantly shortened by increasing daylength