Mule deer (Odocoileus hemionus), domestic sheep (Ovis aries), and American black bears (Ursus americanus) were fed quebracho (Schinopsis sp.) tannin to determine the contribution of salivary proteins to nitrogen- and fiber-digestive efficiencies and tannin metabolism. These values were compared to previously published values for laboratory rats (Rattus rattus) and prairie voles (Microtus ochrogaster). Mule deer, black bears, and laboratory rats consuming this condensed tannin produced tannin-binding salivary proteins that reduced fecal-nitrogen losses per unit of ingested tannin and reduced tannin metabolism relative to domestic sheep and prairie voles. Digestibility of the plant fiber was reduced significantly by tannins in domestic sheep, but not in mule deer. Although virtually all ingested tannin (98.3 ± 5.0%) was recovered in feces of mule deer and black bears, ca. 25% was not recovered in feces of domestic sheep and presumably was metabolized. The defensive role of tannins as digestion inhibitors or toxins is dependent upon the molecular characteristics of the tannin interacting with the physiological capability of the animal. Results from one plant-mammal interaction cannot be used to interpret others without an understanding of the characteristics of the tannins and the physiology, ecology, and evolution of the animal.

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