Sheep Foraging Behavior in Response to Interactions among Alkaloids, Tannins and Saponins

BACKGROUND: A mixture of plant species adds biochemical diversity to pastures that may enhance productivity while decreasing reliance on herbicides and insecticides. All plants contain secondary metabolites (PSMs) that interact in plant communities in a variety of ways. Our objective was to determine if PSM diversity enhanced food intake when sheep were allowed to select from foods that varied in concentrations of tannins, saponins, and alkaloids. We hypothesized that intake of foods containing alkaloids would increase when sheep were offered supplemental foods with tannins and saponins. The alkaloid gramine is proteinaceous in nature, tannins bind to proteins in the gut, which enhances excretion of proteins, so we hypothesized tannins would bind to gramine and enhance its excretion from the body. The alkaloid ergotamine is steroidal, saponins have a high affinity for binding to lipid and steroidal compounds in the gut and then being excreted, so we hypothesized saponins would bind to ergotamine and enhance its excretion from the body. RESULTS: We found that sheep fed either gramine or ergotamine in combination with tannin- or saponin-containing foods had higher intakes of food than sheep offered only foods with gramine or ergotamine. CONCLUSION: These findings are consistent with the hypothesis that animals can neutralize the negative effects of alkaloids by ingesting tannins and saponins. Our results show that PSMs can complement one another to increase a herbivore\u27s intake of unpalatable plant species, with the potential to maintain healthy animals and bio-diverse landscapes