Experimentally induced cartilaginous fractures (osteochondritis dissecans) in foals fed low-copper diets

Four Thoroughbred foals were weaned from their dams when they were 1 day old and were fed a liquid milk-replacer diet containing approximately 1.7 micrograms of copper/g from plastic buckets for 4 to 7 months. They were kept in stalls with fiberglass walls and asphalt floors covered with rubber pads. Serum copper and zinc concentrations were determined 3 times/week by atomic absorption spectrophotometry, and liver copper and zinc concentrations were determined similarly after acid digestion of tissues taken at necropsy. The amount of soluble collagen in articular cartilage and aortic tissue was determined after necropsy. Clinical signs of illness, particularly evidence of lameness, were monitored daily. The foals were weighed weekly, and growth rate was monitored by measurement of height at the withers. Packed cell volumes and total and differential WBC counts were measured each time blood was drawn for copper and zinc concentration determinations. The foals were examined by necropsy at the end of the experiment, and the tissues were examined histologically. The foals developed intermittent, but nondebilitating, diarrhea with the onset of low serum copper concentrations. Considering the totally liquid diet, the foals grew well. Serum copper concentrations decreased to less than 0.1 micrograms/ml in 13 to 16 weeks. Lameness was evident 2 to 6 weeks after serum copper concentrations decreased to their lowest value (less than 0.1 micrograms/ml). All foals developed stilted gaits and ultimately walked on the front of their hooves. Major hematologic changes and alterations of hair color were not evident. Soluble collagen of articular cartilage and aortic tissue increased from 340 to 600% greater than that of control foals.(ABSTRACT TRUNCATED AT 250 WORDS)