Technical Abstract: Consumption of locoweed (Oxytropis sericea) by sheep causes neurotoxicity, but specific behavioral effects have been given little attention. We examined the ability of ewes exposed to locoweed during gestation and/or lactation to discriminate their own from an alien lamb. Ewes (n=6 per treatment group) were fed a 10% locoweed pellet during 1) gestation (day 100 to 130)(LC) but not during lactation; 2) lactation (day 10 to 50 postpartum)(CL) but not gestation; and 3) both gestation and lactation (LL); controls (CC) were fed alfalfa hay. Ewe behavior was examined in a two-lamb choice test on postpartum days 20, 40, and 50 (days 10, 30, and 40 of locoweed feeding). Locoweed feeding increased (P < 0.05) serum AST activity and swainsonine concentration compared to controls, indicating moderate intoxication. Discrimination of lambs was not adversely affected by locoweed exposure. Locoweed intoxication during gestation decreased (P = 0.06) ewe approach times to the first lamb, while locoweed exposure during lactation increased (P < 0.03) approach times to the first lamb. Ewes not receiving locoweed during lactation (CC, LC) were initially (postpartum day 20) slower to approach their own lambs, but on days 40 and 50 had faster approach times to their own lambs compared to CL and LL ewes. Intoxicated ewes displayed an apparent locoweed-induced hypersensitivity and nervousness; these lactating ewes spent a greater percentage of time with their lambs after contact than did controls on postpartum day 50. If clinical signs of toxicity are not severe, culling intoxicated ewes for behavioral reasons may not be warranted.