Technical Abstract: This study investigated whether exposure of ewes to locoweed (Oxytropis sericea) during gestation would affect ewe behavior during parturition, ewe-lamb bonding and related behaviors post partum, and maternal responsiveness of ewes to alien and own lambs. Twenty-nine nulliparous Columbia-Targhee ewes bearing a single fetus were divided into two feeding treatments: (1) locoweed (L, n=15), fed as a 10% locoweed pellet at 3 kg/day from day 100 to 130 of gestation, or (2) controls (C, n=14) fed 3 kg/day of alfalfa hay. Lamb birth weights were reduced about 25% from maternal locoweed ingestion. There was a distinct lack of maternal-infant bonding due to locoweed intoxication of lambs. Only 1 lamb born to L ewes was able to nurse without assistance within 120 min. Lambs born to L ewes took longer to stand (P < 0.05), to initiate teat-seeking behavior (P < 0.03), and to suckle (P < 0.0007). The behavioral toxicosis did not persist in lambs, as behavioral anomalies largely disappeared within 10 days following parturition. Locoweed-intoxicated ewes in general had an increased propensity (P < 0.1) for locomotor activity, notably during fetal expulsion, and longer fetal expulsion times (P < 0.1). There were few behavioral differences induced by locoweed up to 30 min post partum, when L ewes became inattentive to lambs (P < 0.1). After the first (human assisted) suckling bout, L ewes were attentive toward both their own and alien lambs. Both L and C dams were equally aggressive toward alien lambs. These results indicate that lamb survival after maternal locoweed exposure will depend greatly on human intervention. If locoweed-exposed lambs survive the first 24 to 48 hours after birth, then the prognosis for survival improves greatly.