Diterpene alkaloids - methyllycaconitine and nudicauline. The alkaloids act principally at the neuromuscular junction causing a curare-like blockade with resulting muscle weakness and paralysis.
Foothills larkspur appears to be most toxic in the preflowering stage. There is however considerable variation in the toxicity of the plant from year to year.
Larkspurs are erect, perennial, herbaceous plants with simple or branched hollow stems; the leaves are alternate and palmately divided. The flowers are perfect and irregular, and are carried in terminal racemes. The flowers are dark blue in color. There are 5 sepals, the upper most one having an obvious spur. The corolla comprises two sets of two petals each, the two lower ones forming a claw and the upper two extending into the spur. The flowers have multiple stamens and 3 pistils which may be fused at the base. The fruits are follicles that split open to release numerous dark brown/black seeds.
Intestinal stasis and bloat.
Avoid stressing the affected animals. Gently herd the cattle away from the larkspur area. Where possible give physostigmine intravenously (0.08mg/kg)with as litle stress as possible. Keep the animal on its sternum to reduce bloating, and if necessary treat the bloat by passing a stomach tube, or by trocarizing the rumen.
Sudden death due to respiratory paralysis. Stressing the animal hastens death.
Muscular paralysis due to the neurotoxic alkaloids binding to acetylcholine receptor sites causing muscular paralysis.
Sudden death is often the presenting sign of larkspur poisoning. Evidence of the animal having grazed the larkspur, or identifying the plant in the rumen contents is helpful in diagnosis.
Sheep are resistant o the effects of larkspur alkaloids and are useful biological controls. Allowing sheep to graze the larkspur ahead of cattle reduces the risk of the larkspur poisoning in cattle.