Final answer:
Exposure to black walnuts can cause laminitis in horses, which is a painful inflammatory condition of the hoof that can lead to severe lameness(option a).
Step-by-step explanation:
Exposure to black walnuts can cause a serious health issue in horses known as option a) laminitis (Founder).
Laminitis is a painful condition in which there is inflammation of the sensitive layers of tissue (laminae) inside the hoof in horses. This can lead to severe lameness and can be triggered by ingestion of black walnut shavings or bedding. It is important for horse owners to recognize the signs of laminitis which include reluctance to move, heat in the hooves, and increased pulse in the feet and seek immediate veterinary care if they suspect their horse has been exposed to black walnuts.