Reindeer (Rangifer tarandus tarandus) and Forest Reindeer (Rangifer tarandus fennicus) are unique northern ruminants. They have distinctive and prominent adaptations for surviving in harsh, seasonal environment. Even in captivity, far away from their native habitats, they show physiological changes aimed to respond to seasonal changes. Because of this they need appropriate, seasonal diets in captivity. In this article we will cover the basics of reindeer nutrition. In next articles we will dive more deeply in to summer and winter diets and finally we will look at how this can be managed in captivity to have healthy animals.
R.t.tarandus and R.t.fennicus are subspecies of the reindeer Rangifer tarandus. They differ in appearance in that the forest reindeer has longer legs and narrower antlers. Their diet is thought to be similar, though there is insufficient data on forest reindeer’s natural diet. Some estimation can be made based on what type of forage is available in Finnish forests and wetlands. In captivity both subspecies seem to thrive on the same diet. In this article we talk about reindeer nutrition, but this can be applied to both subspecies equally.
How do they eat?
Before we can address the diet of reindeer, we need to look at their digestive system and strategies. So far, we have established that reindeer is a ruminant, meaning that it relies most of its digestion on microbes living in its forestomaches. When we feed a ruminant, we are feeding its gut microbiota, which turn feed they eat into units the ruminant can use. Most important ones are volatile fatty acids (VFA’s) for energy and microbial protein what basically means dead microbes that leave the forestomaches and get digested and absorbed by the ruminant.
Ruminants can be classified as browsers, intermediates or grazers. Instead of individual boxes these classifications are more like a spectrum where a ruminant species is placed based on its diet and some physical characteristics of its digestive tract. Many of the intermediate ruminant species can move along this spectrum to adapt to changes in food availability in their habitat. Species in each extreme are more fixed to their strategy. Reindeer is one of these intermediate ruminants that can travel along the spectrum. This makes it an adaptable survivor of the north.
Rangifer tarandus has an almost circumpolar distribution across the northern countries. Seasons are very distinctive in these areas: winter is long, dark and cold where as summer is short, light and warmer. In the summer the vegetation is plentiful, fresh and nutritious. In the winter there isn’t nothing much to eat, so reindeer has adapted to eat lichen that can be uncovered from snow. Reindeer move in large heard that can have tens of thousands of individuals. They move between winter pastures and summer calving grounds/summer pastures.
In order to survive on changing diet the reindeer has to be able to conserve energy and protein in the winter and accumulate body reserves during the summer. Physiological changes in metabolism that happen to facilitate survival need to happen before the amount of food starts to decrease in the late autumn. If decreasing food would be the trigger to start the process of moving to winter metabolism, it would be too late and energy would be lost. For this reason, the metabolic changes are regulated by hormonal cascade that is regulated by melatonin. Melatonin production is regulated by the amount of light, and in the north the changing amount of light is a big and visible indicator of changing season.
In the winter the reindeer eat less, spend less time foraging for food and their energy balance is negative through the winter. Reindeer start to mobilize body reserves accumulated during summer and autumn. The calves growth arrests during winter, because just the maintenance of body functions takes all the energy available. They continue growing when the energy balance is turned to positive again. In the winter there is little food available and digging it up from snow can take a lot of energy. Especially late winter is a time of famine.
When winter turns to spring and summer the amount of light begins to increase. Food intake and foraging increase and the reindeer start a migration to their summer pastures. In the summer they eat more food that is more nutritious than in the winter. During summer and autumn they accumulate body reserves to help them make through next winter.
Now we have covered the basic idea of reindeer nutrition. Most important things to remember are:
- Reindeer is an intermediate ruminant
- Reindeer’s habitat changes tremendously between seasons
- To survive in changing environment the reindeer has to change its diet
- Physiological changes happen whether or not the diet changes
- Summer is nutritionally important because body reserves determine survival in winter
Next we will dig in to summer and winter diets in the wild. See you there!
P.s. If you have questions or comments don’t be afraid to shoot me a message! Contact me here or email aino [a] feralanimalnutrition.com
References & further reading
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