Cattle's grazing of the locoweed Wahweap milkvetch (Astragalus lentiginosus var. wahweapensis) was evaluated on desert and foothill winter range during the winter of 1986 to 1987. Dry, dead stalks of Wahweap milkvetch that had grown in 1985 and 1986 made up 15% of cattle diets overall, and 24% of diets when cattle grazed gravelly benches where it was abundant. Nutritional quality of Wahweap milkvetch was higher than of most associated forage, but its alkaloid concentration varied among the senescent stages. One cow aborted and two cows developed clinical signs of locoweed poisoning, including water belly (hydrops amnii). Microscopic lesions consisting of cytoplasmic foamy vacuolation were evident in both the dam and fetus. Because senescent stalks of Wahweap milkvetch are palatable and readily grazed by cattle, ranchers should not permit cattle to graze infested sites until other green forage is available in the spring.