2.1. Ecophysiological characteristics of reindeer

The reindeer (Rangifer tarandus) is a species of Cervidae that inhabits the whole northern circumpolar area, spreading from the North America to Eurasia (Banfield 1961). Reindeer herding is a centuries long tradition, a substantial livelihood, a cultural activity, and a way of life among a number of peoples in northern Fennoscandia and Eurasia. The Fennoscandian semi-domesticated reindeer is believed to have descended from the wild Eurasian mountain reindeer (Rangifer tarandus tarandus L.) (Siivonen 1975). Reindeer herding obviously developed from wild reindeer hunting, and reindeer have been herded by the Sami people in northern Fennoscandia for probably 1000-1500 years, or even longer (Banfield 1961, Ingold 1980, Eira 1984). The selection process has differentiated the reindeer from its wild ancestor by producing reindeer that are more easy to handle and have some differences in behavior and appearance, but can breed and produce offspring with the wild conspecies. Reindeer graze freely on natural pastures during most of the year and they are gathered only during certain periods of the year for calf branding and slaughtering. During the past few decades, reindeer herding has undergone significant changes, including the establishment of calf slaughter, increased subsistent feeding during winter, antiparasitic treatments, as well as many technical developments. However, the survival of reindeer is still highly dependent on natural conditions. The problems in the survival of reindeer are basically similar to those of other freely grazing northern species, and the success of the animals depends how successfully they calve, grow during summer, and survive over winter.

The reproduction of reindeer is strictly seasonal: the hinds get pregnant in autumn, gestation lasts throughout the winter (ca. 220 days), and the calves are born during spring. There are about 0.7 million semi-domesticated reindeer in Finland, Sweden and Norway, with approximately 300 000 new calves born every year. The reindeer calves are well developed and capable of effective thermoregulation after birth (Hissa et al. 1981, Markussen et al. 1985, Soppela et al. 1986). The digestion of the newborn calves is essentially monogastric until their forestomachs become used to the fermentation of green vegetation. The nutrition of the calves during the first weeks of life relies on milk that is rich in protein and lipids (Luhtala et al. 1968). Reindeer calves grow very quickly during the peak suckling period and their first months (Timisjärvi et al. 1982). During summer and autumn, reindeer eat various highly nutritious plant species and mushrooms (Nieminen & Heiskari 1989), accumulate body protein and fat, and increase their body weight. Calves usually accumulate little fat during their first summer and are typically lean (Ringberg et al. 1981). The main winter feeds of semi-domesticated Fennoscandian reindeer in many areas are ground lichens (Nieminen & Heiskari 1989). Lichens supply enough energy to maintain the reindeer over winter, and keep water intake and its thermal costs at a low level (Soppela et al. 1991) but do not prevent undernutrition in which a negative balance of nitrogen occur (Ryg & Jacobsen 1982).

During winter, reindeer save nitrogen by decreasing the filtration rate of kidneys (Valtonen 1979) and may use adipose tissues as an additional source of energy (Ringberg et al. 1981, Larsen et al. 1985) but lose about 20 % of their body weight even in normal conditions (Nieminen et al. 1984). Pregnant hinds use their body fat stores mainly for foetal growth (White & Luick 1984, Tyler 1987). Similarly to other large northern species that are active throughout the winter (Scholander et al. 1950), reindeer are well adapted to tolerating low ambient temperatures, principally because of their prime fur insulation (Timisjärvi et al. 1984, Nilssen et al. 1984b), and by peripheral cooling of the lower parts of their legs (Irving & Krog 1955) and nasal cavities (Johnsen et al. 1985). By the means of various thermal adaptations, reindeer tolerate ambient temperatures as low as -30 °C or lower during winter without increasing their heat production (Nilssen et al. 1984b).