No abstract

Mink (Mustela vison) were treated during the period of embryonic diapause with prolactin or ergocryptine (CB-154). Prolactin advanced implantation time and hastened onset of luteal phase progesterone secretion. Duration of gestation in prolactin-treated adult mink was shorter than that of control mink. Ergocryptine had the opposite effects, prolonging gestation and inhibiting onset of luteal phase progesterone secretion. Prolactin is suggested to be the luteotrophin necessary for termination of embryonic diapause in mink.

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<.

The influence of light on fur growth and reproduction in the mink has been investigated. Exposure of kits and adults to 4L/20D (4 light hours/20 dark hours) after completion of the summer furring cycle accelerated the development of the winter pelage. Gradually increasing the length of the daily photoperiod after growth of the winter pelage had been completed also hastened the onset of the breeding season. An abrupt change from 4L/20D to 16L/8D either inhibited gonadal development or initiated gonadal atrophy. It was also noted that mink changed from a 4L/20D schedule to a 16L/8D schedule immediately after completion of the winter furring cycle failed to begin development of the summer pelage for 10 to 12 weeks. This observation suggests that a refractory period exists in the initiation of growth of the summer pelage. However, a similar experiment conducted after completion of the summer pelage showed that the animals responded immediately to decreased light by molting into the winter pelage. It was also noted that changes leading to the development of the summer pelage occurred concomitant with or slightly after the initiation of testicular regression, while gonadal recrudescence occurred after completion of the winter furring cycle. The significance of these observations in relation to possible hypophyseal mechanisms for their control is discussed.