Black walnut (Juglans nigra) toxicosis: A model for equine laminitis

Twelve light horse geldings developed laminitis within 8 to 12 h of being dosed by nasogastric tube with an aqueous extract of black walnut (Juglans nigra). Four of the 12 horses developed the severe signs of grade 3 laminitis (lame at a walk, refused to lift feet). Laminitis was accompanied by mild depression and limb oedema. There was no evidence of shock or colic. The horses developed neutropenia by 4h after dosing with the extract, which shifted to a relative neutrophilia by 8 to 12h. Minimal increases in plasma epinephrine and cortisol concentrations were suggested in severely affected horses. Severe laminitis was characterized by necrosis of dermal tips of dorsal primary epidermal laminae. A proliferative epithelial response in these laminae was distinguished by numerous mitotic figures and clusters of epithelial cells. This evidence suggests that black walnut toxicosis is not only a consistent clinical model, but is also a reliable clinico-pathological and pathological model for study of the pathogenesis and treatment of laminitis.