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Horses
and Black Walnut Shavings Late one night last winter, my neighbour called to tell me his mare had suddenly become lame. What he described was the typical saw horse stance of a horse with laminitis (founder). the mare would not move. She is a middle aged quarter house which is fed only a grass hay and has a run in shed for housing. No grain had been fed in the last month and there was none in the barn that she could accidentally obtain. This is not a typical history for a horse with feed induced laminitis. On further questioning, the neighbour indicated that he had bedded the horse with shavings two days before. The shavings were obtained from a nearby hardwood furniture factory. On questioning, he indicated that the plant was planing black walnut boards while he was at the factory. Examination of the shavings indicated that about 20% of the shavings were dark or black, typical of black walnut. The mare was treated by removing the shavings from the stall; washing of the legs to reduce any further absorption of toxin; and cycling between cooling of the legs by packing them with snow for half an hour followed by allowing them to warm up for half an hour. The core body temperature of the horse was originally 39.5 degrees C, but returned to a normal 38 degrees C within 2 hours. The mare completely recovered with no permanent damage. Black walnut (Juglans nigra) is native to southwestern Ontario and has been planted as a cultivated tree. Clinical signs of laminitis typically occur with one to two days of exposure to shavings containing as little as 20% of black walnut shavings. Horse owners should be very careful when purchasing or being given shavings from unknown sources. Further information on plant poisonings can be obtained from the Canadian Poisonous Plants Information System at the Internet address listed below: Munro,
Derek B. For more information...contact Dr. Robert Wright at rwright@omafra.gov.on.ca
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