Mesquite Tree Beans Toxic?

Q. My horse recently had a horrible colic episode due to mesquite tree beans. Every summer these trees produce large bean pods, which evidently taste like candy to horses. According to my vet, they also slow down gut motility--hence the colic. I have lived in Texas with horses and mesquite trees all of my life, and I have never before heard of a horse getting sick from eating the beans. Since the colic, I have looked up "horses and mesquite trees" everywhere and have not found one article about mesquite beans being harmful to horses. Do you have any information on this?


A. Mesquite is a common shrubby tree of the Southwest. In many areas, cattle eat the beans when other food supplies are low, and the beans can help sustain animals in times of drought. The beans are high in carbohydrates and are an energy source. Some years, massive numbers of beans are produced by the mesquite trees.

The problem arises when excessive amounts of the beans are eaten; they can cause rumen impactions in cattle, and a severe acidosis results from the fermentation of the beans in the rumen. Horses which eat large quantities of the beans might also develop colic as a result of the beans causing an impaction of the stomach or intestine. Surgery might be needed to remove the impacted mass of pods and beans.

About the Author

Anthony Knight, BVSc, MS, Dipl. ACVIM

Anthony P. Knight, BVSc, MS, Dipl. ACVIM, is a professor of large animal medicine in the College of Veterinary Medicine and Biomedical Sciences at Colorado State University. He received his veterinary degree from the University of Nairobi, Kenya, in 1968. After completing a master’s degree at Colorado State University, he joined the faculty in 1974. His current professional interests include livestock heath, foreign animal diseases, emergency management, and plant toxicology. He has written two books on poisonous plants of animals in North America, and maintains a poisonous plants website for use by anyone wanting poisonous plant information.

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