On the consumption of REE-rich carbonate earthy substances by ungulates on the western shore of Lake Baikal.

Geological and hydrobiogeochemical studies were carried out in the valleys of the Sredniye Homuty and Hargino streams on the western shore of Lake Baikal in order to find the reason for the active consumption of carbonate and clay-sandy earths by wild ungulates there, which were found to be enriched with forms of rare earth elements (REE) that are easily extracted in a slightly acidic (HCl, pH-2) environment. The studies revealed that the prevalent mountain-taiga landscapes in the study areas, which were formed mainly on carbonate rocks, were characterized by low Na content, an abnormal ratio in feed Ca:Mg:P = 3:1:1 with a norm of 0.6:1:1, as well as extremely low REE content (average with Y and Sc = 0.25 ± 0.11 mg/kg). The average Na content in dry grass (Carex sp., N = 20) in the study area was 0.0431 ± 0.012 g/kg. On average, the amount of Na available to animals in carbonate kudurits were found to be comparable to its content in local dry vegetation. However, the average amount of REE extracted from kudurits (13.461 mg/kg) under abomasum conditions is 50 times higher than in plant feeds. The combination of our comprehensive analytical studies and a review of the literature on the role of REE in the body of mammals suggest that geophagy may be driven by the need to acquire certain trace elements, primarily rare earth elements, which appear to be closely associated with the neuroimmunoendocrine system.