Sheep can and do reduce levels of internal parasites by eating plants high in tannins. Offering growing lambs two compounds tannins and saponins is likely to increase food intake, but will it also reduce the number of internal parasites in lambs?
Lambs were 80 days of age at the beginning of the trial. Lambs that were infected with the internal parasite Haemonchus contortus (common names: red stomach worm, wire worm or barber’s pole worm) were fed a: 1) control (C) diet, 2) C plus tannin (T), 3) C plus saponin (S), or 4) a choice of T and S. A fifth group was also fed a choice of T and S, but not infected with parasites.
Animals offered a choice of S and T whether or not they were infected with parasites ate more food and gained more weight than animals offered T or S alone. However, sheep offered a choice had greater fecal egg counts (an indirect measurement of parasite loads) than sheep fed T or S.
In this study, parasite load was considered light, but still required treatment. Offering lambs a choice between saponin- and tannin-containing foods allowed them to increase nutrient intake and gain more weight but did not help them reduce their parasite load. For growing young lambs gaining weight and maximizing nutrient intake may be more important than reducing parasite load provided the parasite infection is not too high.
Reference: Conpani, G, J.O. Hall, J. Miller, and J.J. Villalba. 2013. Plant secondary compounds as complementary resources: Are they always complementary? Oecologia: in press