Saponins are compounds found in a number of plants. Structurally they are an aglycone nucleus with one or more carbohydrate side chains. A source of saponins is the plant Quillaja saponaria. Quillaja saponins (QS) are used as vaccine adjuvants due to their ability to potentiate and modulate immune response. Oral and s.c. administration of QS with an antigen can modulate the immune response, including enhanced antibody and cytokine production (Cainelli Gebera et al., 1995; Hoshi et al., 1999). Turner et al. (2002) investigated feeding a crude Q. saponaria extract to weaned piglets challenged with Salmonella typhimurium. No differences in pig performance or serum antibody concentrations were ob-