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Forage from a sagebrush-dominated winter range and rumen ingesta from mule deer wintering on this range were analyzed for monoterpenoids. The average monoterpenoid level of the rumen ingesta was 0.3%, compared with an average of 1.64% expected from the proportion of monoterpenoid-containing plants in the diet. This 80% reduction between the monoterpenoid level from the rumen compared to the level expected from the ingested forage was highly significant (p<.01). The exact method in which the monoterpenoids are lost from the ingesta was not determined, but evidence from other studies suggests that monoterpenoids may be lost from ingested forage as early as the mastication process. The amount of monoterpenoids found in the rumen ingesta at the time of sampling does not appear to be high enough to interfere with microbial activity. This loss of monoterpenoids may explain the conflict between in vitro evidence that big sagebrush monoterpenoids inhibit rumen microorganisms and digestive trials which show that big sagebrush is a highly digestible winter forage. This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries. The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact lbry-journals@email.arizona.edu for further information. Migrated from OJS platform August 2020