ovulations took place prior to these brief luteal phases. The shape of the progesterone Ž
. curves was, as also found in sheep, highly variable Ryan et al., 1991 .
The fact that some females were still reproductively active in mid-February could explain the fact that late pregnancies can occasionally be seen at slaughter in August.
Ž .
McEwan and Whitehead 1972, 1980 documented that the reproductive seasons in reindeer and caribou may last up to150 days. These results are in accordance with those
reported in various deer species and reindeer where the cyclical production of proges- Ž
terone has been found to last for about 4–5 months Asher, 1985; Curlewis et al., 1988; .
Knox et al., 1988; Ropstad et al., 1995 .
3. The oestrous cycle
Ž .
In the experiment described by Ropstad et al. 1995 the overall average oestrous Ž
. cycle length was 19.4 5.7 days SD, range:13–33 days . The average length of the
Ž
y1
. follicular phase plasma progesterone - 1.6 nmol l
remained fairly constant at about Ž
. 3 days over the same period overall mean SD s 3.0 1.6 days . An average oestrous
Ž .
cycle length of about 20 days was found also in adult females Ropstad, 1998 . The detailed endocrine profiles of the oestrous cycle in reindeer are generally in
Ž .
accordance with those found in the ewe, extensively reviewed by Goodmann 1993 . Ž
. 15-Ketodihydro-PGF
was secreted in a pulsatile manner Ropstad et al., 1995 . The
2 a
first pulse was recorded before progesterone declined to basal levels, suggesting that PGF
is the main luteolytic factor also in reindeer. In two animals the preovulatory LH
2 a
Ž
y1
. peak occurred 66 and 42 h after progesterone had reached basal levels - 1.6 nmol l
. Ž
y1
. In both animals the maximal oestradiol level 16–18 pmol l
preceded the preovula- tory LH peak. The duration of the LH peak was 12 and 15 h, respectively. Plasma
Ž progesterone concentrations were found to be higher than baseline levels 1.6 nmol
y1
. l
99 and 78 h after LH maximum in two females. 3.1. Effect of cloprostenol in nonpregnant females
Treatment of nonpregnant females with cloprostenol resulted in an immediate and Ž
. rapid decrease in plasma progesterone concentrations Ropstad et al., 1996a . The
Ž .
plasma progesterone remained low for a varying period of time 100–150 h until the onset of a new luteal phase. The fall in plasma progesterone was associated with
increases in 15-ketodihydro-PGF . Generally, the concentrations of 15-ketodihydro-
2 a
Ž
y1
. PGF
were lower than during normal luteolysis 400–600 pool l and a pulsatile
2 a
secretion pattern was not seen. The fall in progesterone was accompanied by rises in Ž
y1
. plasma oestradiol peak values: 16–31 pool l
. A preovulatory rise in plasma LH was seen immediately after the increases in plasma oestradiol. The time elapsing between
cloprostenol treatment and the preovulatory LH peak ranged from 48 to 72 h. 3.2. Oestrous symptoms
Oestrus, indicated by standing behaviour, was observed in three females as a result of Ž
. cloprostenol treatment Ropstad et al., 1996a . The time elapsing from induction of
luteolysis till the first observed oestrous symptoms was 56 and 60 h in one female and Ž
. Ž
69 h in another. The average duration of standing behaviour oestrus was 27 h range: .
24–30 h . General interest in the observer, and lifting of the tail in response to touching the perineal regionrvulva, were seen for a somewhat longer period, usually 3–6 h prior
to and after the standing behaviour. No vaginal discharge or swelling of the vulva was observed during oestrus.
4. Pregnancy
