EFFECTS OF MELATONIN IMPLANTATION OR ARTIFICIAL LONG DAYS ON SEASONALOVULATORY ACTIVITY IN ROE DEER (CAPREOLUS-CAPREOLUS L)

Three experiments were conducted to determine the effects of melatonin implantation or photoperiodic changes after the winter and summer sol stices on the onset and cessation of the annual ovulatory season in th e female roe deer. In the first experiment five adult female roe deer received melatonin implants from 16 April. Three females were kept as controls and received no melatonin treatment. Treatment induced a rapi d and sharp decrease in prolactin concentrations and advanced the ovul atory period by 72 days (first progesterone increase: 4 June versus 10 August in melatonin-treated versus control females, respectively; P=0 .022). In the second experiment four adult female roe deer received me latonin implants on 13 January. Because of the natural presence of a p ersistent corpus luteum in the female roe deer, females received month ly injections of prostaglandin analogue in order to determine if they were able to re-ovulate after induced luteolysis. Last date of elevate d progesterone concentration was observed later in melatonin-treated f emales than in non-melatonin-treated females of the preceding year. In the third experiment, four adult females were kept in light-proof roo ms and exposed to long days (16L(light):8D(dark)) from the summer sols tice. Exposure to long days delayed by 46 days the first ovulation (fi rst progesterone increase: 14 October vs. 28 August in long-day-treate d vs. control females, respectively; P = 0.014). Treatment of female r oe deer with melatonin implants in April can induce a substantial adva nce of ovulatory activity; prolonged exposure to melatonin after 13 Ja nuary extends the sexual season and ovulation was delayed in females e xposed to long days after the summer solstice. These results suggest t hat the female roe deer initiates its breeding season in August after perceiving shortening days and ends it in February after perceiving le ngthening days.