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Skeletal Changes in Hemochromatosis of Salers Cattle

Department of Microbiology, Immunology and Pathology, and Veterinary Diagnostic Laboratory, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO (RWN, KJH); and Wyoming State Veterinary Laboratory, University of Wyoming, Laramie, WY (DOT)

Hemochromatosis is an inherited defect in Salers cattle, characterized by increased iron absorption and wasting in young animals. Loss of teeth and soft bones has been reported. This study details bone changes in a prospective study of an affected Salers heifer and an age-matched, half-sibling control. The heifer fell 2 weeks before euthanasia, developed non–weight bearing lameness, and then became recumbent. At necropsy, the heifer was smaller than the control and had fractures of the humerus, femur, and ribs. Distinctive circumferential laminations in the outer third of the cortex were seen radiographically as layers of variably decreased density. In midshaft cross sections, the cortex was wider in some long bones, and fluorescent labeling revealed irregular and intermittent mineralization in the outer cortical layers. Mineral apposition rates in osteons of the inner cortex were decreased as compared with the control, and longitudinal bone formation at the growth plate was markedly decreased. Histologically, there were buried layers of osteopenic, poorly mineralized plexiform bone in outer circumferential lamellae. There was stainable iron in woven bone cores of the matrix. Iron was found in occasional osteoclasts as well. The mandible was severely affected, with loss of cortical bone as well as trabecular bone around the teeth and resorption of dental roots. Bone analysis revealed iron levels in the affected calf that were 30–50 times greater than the control and decreased percent ash in the outer cortex. These results indicate that periosteal dysplasia and osteopenia are responsible for pathologic fractures and tooth loss.

Key words: Hemochromatosis; hyperostosis; hypomineralization; osteopenia; pathologic fractures; periosteal dysplasia; Salers cattle.

Request reprints from Dr. R. W. Norrdin, Department of Microbiology, Immunology and Pathology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523 (USA). E-mail: rnor-rdin{at}colostate.edu