When Your Horse Thinks He's a Termite...

Q: Is chewing pressure-treated wood (the green-tinged wood) dangerous for horses?


Q: Our horses have started eating our fences and tree bark quite frequently this year. They run on pasture, get 10% sweet feed once a day, and have salt blocks all over the pasture. Are they missing a supplement or vitamin?


A: Wood chewing increases if the horses' access to forage is limited; if they have inadequate feed and/or fiber in their rations; in cold, wet weather; or if the horses are confined and bored. Has the horses' quality of pasture, type of hay, or activity level changed?

Mineral imbalances are not known to affect wood chewing, though a salt deficit will increase licking and/or chewing of abnormal substances in the horse's attempt to meet his salt needs. In previous studies, we found that wood chewing was also a highly individual activity--only two or three horses in a group of 10 did 90% of the chewing we observed. If a new horse was put into the herd that was a wood chewer, that could have triggered increased activity in others.

Most types of wood are usually not dangerous, though destruction of fences and barns and the danger of ingesting nails or staples are real problems. Pressure-treated wood, however, has arsenic and other heavy metals that can be harmful if large quantities are consumed. It is best to prevent horses from chewing pressure-treated boards.

Even wild horses chew the bark off trees, but the bark of some trees is potentially harmful--these trees include all members of the cherry family (wild and domestic), peach, black walnut, black locust, and certain types of pine.

About the Author

Sarah Ralston, VMD, PhD, Dipl. ACVN

Sarah L. Ralston, VMD, PhD, Dipl. ACVN, Associate Director-Teaching of the Rutgers Equine Science Center and an Associate Professor in the Department of Animal Sciences at Rutgers' School of Environmental and Biological Sciences, specializing in equine nutrition. She also leads the Young Horse Teaching and Research Program at Rutgers, in which students are actively engaged in training and nutrition/behavior research with yearling to 2-year-old horses. Her current research is focused on the effects of diet on metabolism, behavior, and the development of orthopedic disease in young horses, and she has additional interests in nutritional modulation of stress, metabonomics (the study of metabolic responses to drugs, environmental changes, and diseases), and pasture management. Previous research highlights were the pioneering work she did in nutrition for geriatric horses and post-surgical colics while at Colorado State University in the 1980s, and the discovery of the correlation of hyperinsulinemia with development of osteochondrosis in young Standardbreds.

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