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Cornell University and U. S. Department of Agriculture, Ithaca, NY 14853
4 To whom all correspondence should be addressed.
Abstract
Reproductive organ development, plasma sex steroid concentrations and fur growth patterns were determined for pubescent and adult mink of both sexes, at 1- ta 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 uterine 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<.05) on March 18 and was maximal on April 8 during initiation of implantation. Progesterone then decreased continually and reached near-basal concentrations following parturitions (May 4 to 11). These data suggest the possibility that sexual receptivity in mink may be a response to declining estrogen and that the changing photoperiod during the vernal equinox may be an environmental trigger for initiation of luteal function and termination of the embryonic diapause.
Winter fur growth development was complete by November 10 in all animals and was not affected by ovariectomy of females during anestrus.
Plasma androgen concentrations in males were low from July to September and increased during October and November prior to the first observed increase in testis volume in December. Androgen concentrations were maximal in January and declined continually thereafter. Concentrations decreased prior to, during and following the breeding season. In contrast, testis volumes increased to maximal values on March 3 at the time of initial breedings and declined slowly thereafter. The slow decline in plasma androgen prior to matings and the sharp declines following matings suggest the possibility that androgen withdrawl may induce male sexual activity and that mating itself may further suppress androgen secretion.
1 Present address: Department of Animal Science, Cornell University, Ithaca.
2 Present address: Department of Physiology and Physical Biology, New York State College of Veterinary Medicine, Cornell University, Ithaca.
3 Present address: U. S. Sheep and Fur Animal Experiment Station, SEA, Cornell University, Ithaca.
4 The gratitude of the authors is extended to the Mink Farmers Research Foundation for their continuing support of these investigations. We also acknowledge the animal care provided by Mr. William Gardner, Sr. and Mr. Russell Cole. The antiserum to estrogen was a gift of Dr. B. V. Caldwell, Yale University. The antiserum to progesterone was kindly provided by Dr. K. Kirton, the Upjohn Co. The antiserum to testosterone was obtained from Dr. M. Shemesh, Cornell University.
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  M. Jallageas, J. Boissin, and N. Mas Differential Photoperiodic Control of Seasonal Variations in Pulsatile Luteinizing Hormone Release in Long-Day (Ferret) and Short-Day (Mink) Mammals J Biol Rhythms, December 1, 1994; 9(3-4): 217 - 231. [Abstract] [PDF]
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