Ingestion and dispersal of seeds of desirable species by domestic livestock is potentially important as a range improvement practice, but the passage of seed by livestock has only been studied in a fragmented way, particularly for species adapted to rangelands of western North America. The objectives of this research were to examine the effects of different periods of exposure to in vitro and in vivo digestion processes in cattle on the germinability of several grass species, and determine if the in vitro incubation technique is a good predictor of seed fate following passage through the ruminant digestive tract. Seeds of 13 grass species adapted to the Intermountain West were exposed to in vitro incubation for 24, 48, and 72 hours, and then tested for germination at an optimal temperature regime (10°C night/20°C day) in a controlled environment chamber. Germination responses varied considerably among grass species with changes in length of exposure to in vitro incubation, but germination decreased for incubated seed compared to untreated seed for all species. Five species with the highest germination in in vitro incubation trials were fed to Holstein steers in in vivo digestion trials. Approximately 20% of the ingested seeds were recovered for all species 6 days after feeding, and the highest recovery occurred 2 and 3 days after feeding. Germination of undamaged, recovered seeds decreased as passage time through the digestive tract increased. Of the species tested, seeds of Psathyrostachys juncea, Thinopyrum ponticum, Agropyron cristatum X A. desertorum, and Elytrigia repens X Pseudoroegneria spicata have the greatest potential to survive passage through the digestive tract and germinate in appreciable numbers. The in vitro incubation technique may be used as a crude indicator of seed fate following passage through the digestive tract.