Cyanide Poisoning of Livestock from Cherry Tree Leaves

Severe weather during the growing season can happen at any time, including pop-up thunderstorms or even just an exceptionally windy day. These winds can topple cherry trees or break off limbs into pastures, which are potentially being grazed by livestock now, or will be at some point. Naturally occurring compounds within the plant can be converted to cyanide when the leaves are damaged in some way, like wilting in the case of a downed cherry tree or limb. If cherry trees are within reach of animals in the pasture, beware of wilted leaves, because animals will readily consume them. Animals ingesting wilted cherry leaves experience the release of cyanide (HCN) into the bloodstream, which is a very potent toxin. Cyanide poisoning in livestock is commonly associated with forage sorghums, sorghum-sudangrass, and johnsongrass and is often called prussic acid poisoning, but is also a concern for species like wild cherry and elderberry. 

All animals can be affected by ingesting wilted cherry leaves, but ruminant animals are very susceptible to poisoning from HCN due to an ideal environment within the rumen. According to Toxic Plants of North America by Burrows and Tyrl, as little as 1.2 to 4.8 pounds of wilted black cherry leaves could constitute a lethal dose for a 1,200-pound dairy cow. For a 180-pound sheep, the amount is only 0.18 to 0.72 pounds. The range in dosage is based on the HCN potential of the leaves. There are several factors that need to be considered, but in general, younger leaves have a higher HCN potential than older leaves. Based on this information, our understanding is that the greatest threat to cattle is early in the season. However, normal moisture levels followed by a dry period also tend to increase the HCN potential in cherry leaves. So this issue may repeat itself if we experience a mid-summer slump in moisture.

According to several veterinarians, once the leaves have fallen off the plant, the cyanide levels will drop. However, if the leaves are connected to the plant stems, the leaf tissue can draw toxins from the branches into the leaves. They recommend cleaning the trees out as soon as possible and getting as many of the dropped leaves off the ground before allowing livestock back into the pasture.

Signs of HCN toxicity in livestock can occur very quickly, within 15–20 minutes following ingestion. These may include slobbering, increased respiration, weak pulse, and convulsions. If livestock have collapsed, you may observe kicking or paddling of the legs. Mucus membranes of the animals will be bright red. Livestock will succumb to cyanide poisoning quickly, and death will be rapid.

While the current focus may be on cleaning up downed trees and branches, a long-term goal would be to remove all the cherry trees from the edges of your pastures. This University of Florida herbicide technique factsheet outlines several different techniques that can be used to eliminate woody plants, including cherry trees. Based on the type of treatment you select, it also gives recommendations on specific herbicides and rates to use.

For more reading on the issue of cherry leaves and potential poisoning, read this wild cherry article by Rory Lewandowski from Ohio State University. Additionally, this article on poisonous weeds in pastures from Penn State Extension discusses cherry trees and other potentially toxic plants found in pastures.