Role of Toxins in Intake of Varied Diets by Sheep
Herbivores foraging on toxic plants may consume a variety of foods that contain different toxins to increase food intake and to avoid toxicosis. We studied whether lambs offered two foods, each containing a different toxin, could ingest more food than lambs offered one food with a single toxin. Thirty-two lambs were allotted to four groups that received: (1) a ration with toxin A, (2) a ration with toxin B, (3) two rations, one with toxin A and the other with toxin B, and (4) a ration with no toxins. Toxin pairs used in the study were(1) amygdalin and lithium chloride (LiCl), (2) LiCl and LiCl, (3) sparteine and saponin, (4) oxalate and nitrate, and (5) tannin and saponin. For an hour each morning, lambs were offered their ration(s) and intakes were measured. Lambs were maintained on an alfalfa pellet or grass hay diet. Each trial lasted either five or six days. Whether or not lambs ate more when offered foods with different toxins depended on the kind and amount of toxin in the food. Lambs offered rations with amygdalin and LiCl or oxalate and nitrate consumed more food than lambs offered a ration with only one of these toxins. Lambs offered rations with sparteine and saponin or tannin and saponin did not eat more food than lambs offered a ration with either saponin or sparteine or tannin alone. Nor did lambs eat more when offered two rations both containing LiCl. In all trials, lambs offered toxins showed no signs of toxicosis, and they ate less food than lambs offered rations without toxins. Our results indicate that in some cases ruminants can increase intake of toxic foods by consuming foods containing different toxins. However, currently the only way to determine how specific toxins may interact in the body to influence intake would be to conduct feeding trials using plants or ground diets that contain toxins.
Burritt, E. and Provenza, F. (2000). Role of toxins in intake of varied diets by sheep. Journal of Chemical Ecology, 26(8): 1991-2005.