| Summary: | In vitro fermentation with expressed rumen fluids was used to evaluate the apparent comparative digestibilities of plants ingested by Peary caribou (Rangifer tarandus pearyi) in arctic Canada. The apparent digestibilities of vascular plant components collected in summer and fermented for 60 hours with "summer" rumen inoculum generally were in the range 50-80%, digestibilities of lichens ranged from 18-85%, and those of mosses from 11-35%. In similar trials in which plants collected in the winter were fermented for 60 hours with "winter" rumen inoculum, the green parts of two sedge species were more digestible (65 and 74%) than the corresponding cured leaves (25 and 43%), lichens generally were highly digestible (54-83%), and mosses poorly digested (3-11%). We obtained clear evidence of a seasonal change in the digestive capacity of rumen fluids. Fermentation for periods of 30, 60, and 90 hours revealed that components of vascular plants were digested most rapidly, followed by lichens and mosses. There was no interaction among mixed samples of plants; composite digestibilities approximated expected values based on weighted mean digestibilities of the component species. Peary caribou select forages of high digestibility but they consume, perhaps incidentally, plants of low digestibility when snow or ice restricts their access to the highly digestible species.Key words: caribou, in vitro, microdigestion, arctic plants, rumen, rangifer
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