The Annual Reproductive Cycle of Mink (Mustela Vison)

Abstract

Reproductive organ development, plasma sex steroid concentrations and fur growth patterns were determined for pubescent and adult mink of both sexes, at 1-tc~ 8-week intervals, between July and the following June. Plasma estradiol concentrations and weights (mg/kg) of ovaries, oviducts and uteri decreased slightly in both pubescent and adult females during the first half of anestrus (July to October), then increased slowly throughout the second half of anestrus (October to December). During proestrus (January to February) plasma estradiol concentrations and oviduct weights reached maximum values. During estrus (late February to March) ovarian weights were maximal prior to mating-induced ovulations (before March 11) and subsequently reduced, whereas uteriffe weights continued to increase until implantation (April 8). During estrus, plasma estradiol concentrations prior to mating were reduced (P<.05) from previous peak concentrations and were reduced further following mating. Estradiol remained low throughout pregnancy and lactation. Plasma progesterone remained at or near non-detectable concentrations throughout anestrus, proestrus and estrus, increased slightly (P<.

Advanced implantation in mink (Mustela vison) treated with medroxyprogesterone acetate during early embryonic diapause

“…The MPA values at this time were 3-4 ± 0-3 ng/ml in the treated animals and non-detectable (<0·8 ng/ml) in the controls. On 28 April serum progesterone values were 9-0 and 17-1 ng/ml in 2 pubertal controls, 15 (Enders, 1952) and 7 (Pilbeam et al, 1979) days. The reason for later implantation in pubertal mink is unclear.…”

“…The induction of early implantation by alterations in the photoperiod has also been reported (Hansson, 1947;Holcomb, Schaible & Ringer, 1962;Aulerich, Holcomb, Ringer & Schaible, 1963). We have previously suggested that termination of embyronic diapause and the initiation of implantation occur in response to the changes in circulating levels of progesterone associated with the activation of ovarian progesterone secretion that occurs following the vernal equinox 0022-4 251 /80/010001 -06S02.00/0 (Pilbeam et al, 1979). However, there is no direct evidence that progesterone can induce implantation in mink.…”

“…The reason for later implantation in pubertal mink is unclear. Normal implantation follows the initial increase in progesterone by about 10 days (Moller, 1973;Murphy & Moger, 1977;Pilbeam et al, 1979 …”

“…Corpora lutea do not appear functional on a gross or histological basis until late March (Enders, 1952). Circulating progesterone levels remain low during oestrus, increase at or shortly after the vernal equinox, reach near peak levels about the time of implantation, and fall to low levels around the time of parturition (Moller, 1973;Murphy & Moger, 1977;Allais & Martinet, 1978;Pilbeam et al, 1979). The initial increase in progesterone normally occurs at or after the vernal equinox regardless of the time of mating and ovulation but it can be advanced slightly by alterations in the photoperiod (Allais & Martinet, 1978).…”

“…Various aspects of the annual reproductive cycle and pregnancy in mink (Mustela vison) have been reviewed in detail (Hansson, 1947;Enders, 1952;Asdell, 1964;Venge, 1973Venge, -1974Pilbeam, Concannon & Travis, 1979 (Pilbeam et al, 1979). Corpora lutea do not appear functional on a gross or histological basis until late March (Enders, 1952).…”