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Plasma concentrations of progesterone, oestradiol, LH and 15-ketodihydro-PGF₂ in Norwegian semi-domestic reindeer (Rangifer tarandus tarandus) during their first reproductive season

Blood samples were collected from eleven 1.5 year old female reindeer three times a week from September 1992 until February 1993 and daily in October and November 1992. Blood samples were collected every third hour for a period of three weeks from two females that showed regular oestrous cycles. Plasma progesterone, oestradiol, LH and 15-ketodihydro-PGF₂ were analysed to characterize variations in ovarian function. Reindeer are seasonally polyoestrous. Average duration of oestrous cycles was 19.4 days (range: 13–33 days). Short periods of high progesterone concentrations (4–8 days duration) occurred in five animals before the onset of regular oestrous cycles. The first regular cycle had a significantly longer luteal phase than did the following cycles. During luteolysis 15-ketodihydro-PGF₂ was released in a pulsatile pattern. Maximal oestradiol concentrations preceded preovulatory LH peaks by about 3 h in the two frequently sampled animals. The duration of LH surges was 12 and 15 h, respectively.