Skeletal changes in the ovariectomised ewe and subsequent response to treatment with 17 beta oestradiol

The ewe has been suggested as a suitable large animal model for assessment of therapeutic agents for the treatment of osteoporosis. In this study we asses the response of ewe bone mineral parameters, using dual energy x ray absorptiometry (DXA), after ovariectomy. Regular DXA analysis was performed over a period of 75 weeks followed by a period of dosing with 17 beta oestradiol. Total body bone mineral density (BMD) was reduced in ovariectomised animals 15 weeks post operatively. BMD remained lower than control animals for the entire pre dose period. Subsequently, dosing with 17 beta oestradiol prevented further loss of bone over a period of 38 weeks. Several complicating factors were noted during the study including seasonal BMD variation, a correlation between fat/lean ratio and total body BMD together with a reversible reduction in bone mineral content as a result of lactation. Also changes in BMD were associated with age at ovariectomy.