Larkspur blooms somewhat later than locoweed, usually starting in mid-May, but Knight cautioned that weather has a lot to do with the timing of flowering. A warm spring will result in earlier flowering. According to Knight, flowering time is not only when locoweed is tastiest to livestock, but also when it is most toxic. Horses, cattle, sheep and goats are susceptible, but horses are particularly sensitive. Signs of poisoning don't show up until animals have eaten significant quantities over many weeks.
Animals show a variety of symptoms, including staggering gait and unpredictable behavior.
Sudden changes in behavior, such as rearing and falling over backwards, can make horses unsafe to ride. In cattle, locoweed poisoning causes abortion and birth deformities. There is no specific treatment for locoweed poisoning. If removed from locoweed, animals will show improvement and appear relatively normal after several months. However, horses may not recover completely, making them potentially dangerous if ridden.