Can methane suppression during digestion of woody and leafy browse compensate for energy costs of detoxification of plant secondary compounds? A test with muskoxen fed willows and birch

Digestion and metabolism of woody and leafy browse requires detoxification of plant secondary compounds that can incur an energy cost. Browse, however, inhibits methane (CH4) production and therefore could offset some costs of detoxification. We measured an index of heat increment of feeding (HlFi) and CH4 production in muskoxen (Ovibos moschatus) given a single test meat (at 10 g/kg BM0.75) composed of hay mixed with one of three browse species (Willow: Salix alaxensis, S. pulchra; Birch: Betula nana). Detoxification cost was estimated as HIFi of browse diet-HIFi of hay diet and CH4 compensation as CH4 production of hay diet-CH4 production of browse diet. CH4 compensation was noted in 47% of 15 trials in which a detoxification cost was evident; six trials were with woody browse and one with leafy browse. Separate controls were responsible for the difference in CH4 compensation for leafy browse vs. woody browse. Detoxification costs for twigs and leaves of B. nana were underestimated because of their low digestibility. In only one of six treatments was CH4 compensation documented for B. nana. We conclude that energy saved by CH4 suppression was small (<6%) compared with detoxification costs. (C) 2002 Elsevier Science Inc. All rights reserved.