EFFECTS OF GNRH ON PLASMA LH AND FERTILITY IN MINK

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Abstract
The magnitude and duration of the luteinizing hormone (LH) response to 2 μg gonadotropin releasing hormone (GnRH) in ranch mink during the early mating season was determined by double antibody radioimmunoassay. Elevations in LH were observed at 15 min following treatment. Mean maximum concentration occurred at 45 min post treatment in animals treated early in the breeding season. Administration of GnRH later in the breeding season resulted in a slightly more prolonged response. Electrical stimulation of the cervix had no apparent effect on plasma LH concentrations during the 3 h following treatment. In field studies, administration of 2 μg GnRH followed by a single mating 7 or 8 days later resulted in percent reproductive success (number of females producing litter/number treated) slightly below that of animals mated two or three times. The same dose of GnRH administered within 1 h after the first of two matings had no effect on increasing litter size or percent reproductive success. Administration of a single dose of GnRH either after both matings or after the second of two matings, spaced 1 wk apart, reduced reproductive success by 25–30%. It is presumed that exogenous GnRH interfered with the ovulatory process. Electrical stimulation of the cervix in lieu of first mating resulted in a low-level reproductive success, and was comparable to single mated females in previous experiments.