How It Affects Livestock Larkspur causes heavy cattle losses in western range states. Larkspur is highly palatable to cattle, and losses can be expected when cattle are allowed to graze larkspur-infested ranges, especially where the plant is abundant or grows in large, dense patches. Tall larkspurs increase in palatability as plants mature. Rain, cold fog, or snow showers may lead to greatly increased consumption of larkspur. Losses rarely occur in sheep or horses, but if subjected to sudden physical activity after ingesting large amounts of larkspur, these animals may die.
Plants are most toxic during early growth, but toxicity gradually declines over the growing season.
However, toxin levels may increase in the flowers and pods even late in the season. The toxic substances are mixtures of several alkaloids. These alkaloids and their relative toxicity and concentrations vary between individual plants, at different locations and between larkspur species. The method of toxicity has been identified as neuro-muscular paralysis, leading to respiratory failure, bloat and often death. All parts of all larkspur species are poisonous, but new growth and the seeds contain the highest concentrations of toxic substances.