Germinability and viability of leafy spurge seeds following ingestion by sheep and goats were evaluated. Four sheep and four goats were separated into eight pens and fed individually a known number of leafy spurge seeds. Following ingestion, goats and sheep passed leafy spurge seeds for 4 and 9 d, respectively. Eighteen percent of the seeds fed were recovered in the fecal material of both species of livestock. Number of seeds recovered, expressed as percent of total seeds fed, decreased with time (P < 0.01). Germinability and viability of the recovered seeds were less than the control (P < 0.01). Sheep were more effective than goats in reducing germinability and viability of leafy spurge seeds (P < 0.01). Results indicate that sheep and goats are effective biological tools for reducing spread of leafy spurge seeds. However, animals grazing mature leafy spurge should be confined for 5 d, until all viable seeds have passed through the digestive system, before they are rotated onto pastures that are devoid of leafy spurge.