In winter the horses eat "Salix "spp., "Pyrus communis", "Malus sylvatica", "Pinus sylvestris", "Rosa" spp., and "Alnus" spp. Additionally, Przewalski's horses may dig for "Festuca" spp., "Bromus inermis", and "E. repens" that grow beneath the ice and snow. Their winter diet is very similar to the winter diet of domestic horses, but differs from that revealed by isotope analysis of the historical (pre-captivity) population, which switched in winter to browsing shrubs, though the difference may be due to the extreme habitat pressure the historical population was under. In the wintertime, they eat their food more slowly than they do during other times of the year. Przewalski's horses experience hypodermis in winter, a condition in which their metabolic rate slows down.