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Lupine-induced "crooked calf disease" occurred in a fall calving herd of cows in Northeastern Oregon. Sixty-seven calves from a herd of 131 cows (51%) were born with congenital skeletal malformations primarily of the front limbs, neck, or spine and a few had cleft palates. Because of the nature of the malformations, lupine was suspected, and investigation of the ranch and pastures where cows grazed revealed 2 species of lupine (Lupinus sulphureus; Douglas ex. Lindl. and Lupinus leucophyllus; Douglas ex. Hooker) and poison-hemlock (Conium maculatum). Poison-hemlock was not grazed and therefore eliminated as the teratogenic plant. Extensive grazing of the Lupinus sulphureus especially the seed pods was evident. Chemical analysis of the 2 lupine species demonstrated that L. sulphureus was likely the cause of the birth defects because it contained high levels of the quinolizidine alkaloid anagyrine, a known teratogen. Lupinus sulphureus is a yellow-flowered lupine and contained 1.84% anagyrine in the seed, whereas Lupinus leucophyllus, a purple flowered lupine, contained other quinolizidine alkaloids but no anagyrine. The seed pods of L. sulphureus were high in total alkaloids (42 mg/g of dry seed), of which 45% was anagyrine. After a review of breeding records, grazing patterns and growth stage of plants, it was determined cattle probably ingested L. sulphureus in the seed pod stage during critical fetal developmental periods of gestation. Epidemiologic studies suggested the critical gestational period included day 21 to day 100; 70% of the malformed calves were born to cows that were exposed to the plant during gestation days 60 to 80. The risk of deformities was markedly increased in fetuses exposed during this interval. A few malformations occurred in cows exposed to the lupine as early as gestation day 21 and as late as day 100. We conclude that L. sulphureus was the teratogenic species, and producers should prevent cows from grazing L. sulphureus during gestation days 40 to 100 and consider herbicide control of this lupine species. The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact lbry-journals@email.arizona.edu for further information. Migrated from OJS platform August 2020