OVARIAN FOLLICULAR DEVELOPMENT IN MINK (MUSTELA-VISON)

Ovarian follicular dynamics were studied during the breeding season, b efore and after ovulation in mink. Nulliparous female mink were stimul ated to ovulate with an injection of 4 mu g GnRH. Ovaries from three a nimals were collected on days 0, 2, 3, 4, 5, 6 and 7 after hormone tre atment. A second dose of GnRH was administered on day 8 and ovaries we re collected from three animals on day 9. Corpora lutea and follicles were identified in histological sections and follicles were classified by stage of development, healthy versus atretic, and by diameter. Pre ovulatory follicles (diameter 0.7-1.0 mm) were present in the ovaries of all animals on day 0 and these responded to GnRH treatment by ovula ting. A synchronized wave of follicular development occurred following ovulation. Changes in follicle populations indicated that follicles a re recruited from the small antral follicle class (0.2-0.4 mm) into th e 0.4-0.6 mm class, with the first defined changes occurring between d ays 2 and 4. From the recruited group, a smaller cohort of follicles i s selected to become the dominant follicles between days 4 and 6, and these acquire the ability to respond to a stimulus which induces ovula tion at diameters of > 0.7 mm. The ovaries of unmated mink also contai ned substantial numbers of large, degenerating, luteinized, unruptured follicles. These degenerating, luteinized follicles are considered to represent the demise of large follicles that failed to receive an ovu latory stimulus.