Introduction The breeding season

1. Introduction

Reindeer, like most temperate cervids, are seasonal breeders, with mating coinciding with the decreasing photoperiod in the autumn, and with fawning in the spring. The fact that reindeer are kept under very extensive farming conditions and generally have a high fecundity chiefly explains why little interest has been shown in their reproductive physiology. Reindeer are kept mainly for meat production. One of the most important factors of significance for productivity is the proportion of fertile females that have a calf at foot in Ž . Ž the autumn. Both in caribou Miller and Broughton, 1974 and reindeer Eloranta and . Nieminen, 1986; Lenvik and Aune, 1988 , calf losses ranging from 30 to 50 have been found between birth in the spring and slaughter in the autumn. Investigations by Ž . Lenvik and Aune 1988 indicate a strong relationship between calf losses and the maternal body weight, suggesting that significant reductions in calf losses could be obtained simply by increasing the body weight of females that become mated. In the future, it is likely that reindeer will be managed more intensively and in closer contact with the herdsmen, which implies that there will be an increased need for knowledge on reproduction in this species. Thus, there is a need to expand our knowledge of normal reproductive physiology during the breeding season. Also, there may be benefits from development of methods to control reproduction by hormonal treatment. Little information is currently available about the control of ovarian function during the breeding season and the oestrous cycle. The aim of this paper is to present current knowledge on reproduction in female reindeer with special emphasis on reproductive physiology and the interactions between environmental factors and fecundity. As most reindeer are free ranging and given little supplementary feeding, information based on wild-animal populations is highly relevant to the semi-domestic situation.

2. The breeding season

The plasma progesterone pattern over repeated oestrous cycles during the reproduc- Ž tive season has been described in only a few reports McEwan and Whitehead, 1980, . Rangifer tarandus caribou; Ropstad et al., 1995, Rangifer tarandus tarandus . Both these studies indicate that cyclic ovarian activity occurs from September until February. As a result, the potential reproductive season is considerably longer than is indicated by Ž . the rut, which, is confined to about 2–3 weeks in SeptemberrOctober Lenvik, 1988b . Ž . Reindeer, as sheep Ryan et al., 1991 and other ruminants, are dependent on temporary elevations in progesterone concentration for initiation of regular oestrous cycles. Patterns of short periods of elevated progesterone concentrations were observed Ž . prior to the ordinary luteal phases Ropstad et al., 1995 . These consisted of one or more periods of elevated progesterone concentrations lasting 4–9 days. These results support Ž . Ž findings in caribou McEwan and Whitehead, 1972, 1980 and in reindeer Eloranta et . al., 1990 . The occurrence of LH peaks in three out of five animals indicated that 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