Effects of melatonin implantation or artificial long days on seasonal ovulatory activity in roe deer ( Capreolus capreolus L.)

Abstract

Three experiments were conducted to determine the effects of melatonin implantation or photoperiodic changes after the winter and summer solstices on the onset and cessation of the annual ovulatory season in the 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 rapid and sharp decrease in prolactin concentrations and advanced the ovulatory 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 melatonin implants on 13 January. Because of the natural presence of a persistent corpus luteum in the female roe deer, females received monthly injections of prostaglandin analogue in order to determine if they were able to re-ovulate after induced luteolysis. Last date of elevated progesterone concentration was observed later in melatonin-treated females than in non-melatonin-treated females of the preceding year. In the third experiment, four adult females were kept in light-proof rooms and exposed to long days (16L(light):8D(dark)) from the summer solstice. Exposure to long days delayed by 46 days the first ovulation (first progesterone increase: 14 October vs. 28 August in long-day-treated vs. control females, respectively; P = 0.014). Treatment of female roe deer with melatonin implants in April can induce a substantial advance of ovulatory activity; prolonged exposure to melatonin after 13 January extends the sexual season and ovulation was delayed in females exposed to long days after the summer solstice. These results suggest that the female roe deer initiates its breeding season in August after perceiving shortening days and ends it in February after perceiving lengthening days.