Black walnut fruits consist of a nut surrounded by a thick husk and do not split open when ripe. The toxic phenolic compound, juglone, is found in the bark, wood, nuts, and roots of black walnut. Horses are primarily affected when exposed to shavings that contain black walnut wood. Affected horses exhibit depression, lethargy, laminitis, distal limb edema, and increased temperature, pulse, respiration rate, abdominal sounds, digital pulse, and hoof temperature. Consumption of the shavings may also cause signs of mild colic.
Symptoms usually disappear within a few days after shavings are removed.
Horses on pasture may show mild respiratory signs from pollen or fallen leaves. Leaves are alternate and are spirally arranged along the twig, although they appear to be in two rows. It is patchily distributed throughout the state and is most common in the northeast. In small quantities, yew may be harmless. Canada yew is heavily browsed by deer.