Numerous properties of Yucca schidigera and Quillaja saponaria have been studied with respect to the saponins in the plant. These saponins are present in the extract as well and have been utilized commercially in the food and cosmetic industry for various products. Saponins have detergent-like properties in the presence of water. The detergent-like behavior of saponins plays a major role in their membranolytic properties. In addition, emulsification effects on fat which are characteristic of surfactant-type substances, may occur as well. Three studies were conducted using adult roosters, growing broiler chicks, and growing Japanese quail. Various effects of supplementing Yucca schidigera in the diets of these birds were studied such as: growth performance, overall health, and nutrient availability. An additional experiment was conducted comparing effects of Quillaja saponaria and Yucca schidigera extracts on body weight and fat digestibility in adult roosters. Addition of Yucca schidigera extract to high fat diets (tallow-based) increased lipid excretion in roosters, broilers, and quail. In roosters, dose of yucca extract affected excretion of lipid but no dose effects were seen in broilers or quail. Fat digestibility was not significantly affected by addition of saponins to the diet of adult roosters. However, fat digestibility was reduced in broilers and quail consuming a high fat diet. In general, level of dietary fat seemed to play a role in the effects of Yucca schidigera supplementation in growing birds. Addition of Yucca schidigera to high fat diets resulted in decreased plasma levels of vitamin A and E in broiler chicks. / Graduation date: 2000