Editing Reindeer (section)

=== Seasonal body composition ===
[[File:Svensk ren.JPG|thumb|Sweden]]

Reindeer have developed adaptations for optimal metabolic efficiency during warm months as well as for during cold months.<ref>Karasov, W.H. and Martinez del Rio, C. 2007. ''The Chemistry and Biology of Food in Physiological Ecology: How Animals Process Energy, Nutrients, and Toxins'' (pp. 49–108).</ref> The body composition of reindeer varies highly with the seasons. Of particular interest is the body composition and diet of breeding and non-breeding females between the seasons. Breeding females have more body mass than non-breeding females between the months of March and September with a difference of around {{cvt|10|kg}} more than non-breeding females. From November to December, non-breeding females have more body mass than breeding females, as non-breeding females are able to focus their energies towards storage during colder months rather than lactation and reproduction. Body masses of both breeding and non-breeding females peaks in September. During the months of March through April, breeding females have more fat mass than the non-breeding females with a difference of almost {{cvt|3|kg}}. After this, however, non-breeding females on average have a higher body fat mass than do breeding females.<ref name="Chan-McLeod AC 1999">{{cite journal | last1 = Allaye Chan-McLeod | first1 = A.C. | last2 = White | first2 = R.G. | last3 = Russell | first3 = D.E. | year = 1999 | title = Comparative body composition strategies of breeding and nonbreeding female caribou | journal = Canadian Journal of Zoology | volume = 77 | issue = 12| pages = 1901–1907 | doi=10.1139/z99-169| bibcode = 1999CaJZ...77.1901C }}</ref>

The environmental variations play a large part in reindeer nutrition, as winter nutrition is crucial to adult and neonatal survival rates.<ref>Wilmer, Pat; Stone, Graham; Johnston, Ian (2009). Environmental Physiology of Animals. Wiley. pp. 645–663. {{ISBN|9781405107242}}.</ref> Lichens are a staple during the winter months as they are a readily available food source, which reduces the reliance on stored body reserves.<ref name="Chan-McLeod AC 1999"/> Lichens are a crucial part of the reindeer diet; however, they are less prevalent in the diet of pregnant reindeer compared to non-pregnant individuals. The amount of lichen in a diet is found more in non-pregnant adult diets than pregnant individuals due to the lack of nutritional value. Although lichens are high in carbohydrates, they are lacking in essential proteins that vascular plants provide. The amount of lichen in a diet decreases in latitude, which results in nutritional stress being higher in areas with low lichen abundance.<ref name="Joly Wasser Booth 2015">{{cite journal |last1=Joly |first1=K. |last2=Wasser |first2=S. K. |last3=Booth |first3=R. |date=10 June 2015 |title=Non-Invasive Assessment of the Interrelationships of Diet, Pregnancy Rate, Group Composition, and Physiological and Nutritional Stress of Barren-Ground Caribou in Late Winter |journal=PLOS ONE |volume=10 |issue=6 |at=e0127586 |issn=1932-6203 |doi=10.1371/journal.pone.0127586 |pmid=26061003 |pmc=4464525 |bibcode=2015PLoSO..1027586J |doi-access=free}}</ref>{{rp|6}}

In a study of seasonal light-dark cycles on sleep patterns of female reindeer, researchers performed non-invasive [[electroencephalography]] (EEG) on reindeer kept in a stable at the [[University of Tromsø|UiT The Arctic University of Norway]]. The EEG recordings showed that: (1) the more time reindeer spend ruminating, the less time they spend in [[non-rapid eye movement sleep]] (NREM sleep); and (2) reindeer's brainwaves during rumination resemble the brainwaves present during NREM sleep. These results suggest that, by reducing the time requirement for NREM sleep, reindeer are able to spend more time feeding during the summer months, when food is abundant.<ref>{{cite news |last=Cell Press |date=22 December 2023 |title=Reindeer sleep while chewing their cud |url=https://www.sciencedaily.com/releases/2023/12/231222145453.htm |work=ScienceDaily |location= |access-date=December 25, 2023}}</ref><ref>{{cite journal |last1=Furrer |first1=Melanie |last2=Meier |first2=Sara A. |last3=Jan |first3=Maxime |display-authors=1 |date=December 22, 2023 |title=Reindeer in the Arctic reduce sleep need during rumination |journal=Current Biology |volume=34 |issue=2 |pages=427–433.e5 |doi=10.1016/j.cub.2023.12.012 |doi-access=free |pmid=38141616 |hdl=10037/33347 |hdl-access=free }}</ref>