Osteochondrosis in fetuses of ewes overfed calcium

Summary Ewes were fedad libitum (up to maximum of 2.5 kg/day) a complete feed containing either 1.52% calcium (High Ca) or 0.59% calcium (Normal Ca) on a dry matter basis from day 50 of pregnancy, and the fetuses were removed at 133–135 days. Thyroid C cells, identified by indirect immunofluorescence, were more numerous (P<0.001) and plasma levels of 24,25-dihydroxycholecalciferol [24,25(OH)₂D] were higher (P<0.09) in fetuses of High Ca ewes. These fetuses also had retarded cartilage differentiation in the proximal humeral epiphysis and metaphysis as well as transverse trabeculation in the epiphysis. These entities are two of the hallmarks of osteochondrosis. It was shown that feeding high dietary calcium to pregnant ewes caused osteochondrosis in their fetuses. Hypercalcitoninism and/or an adverse effect of supraphysiological levels of 24,25-dihydroxycholecalciferol may have been contributory to the skeletal abnormalities.