A radiographic study of the extent of variation in cortical bone thickness in soay sheep

In order to assess the effect of nutrition on bone mass, radiographs of metopodia from skeletal collections of Soay sheep (Ovis aries) were taken of animals subject to seasonal stress (from the island of Hirta, Hebrides) and those living in good nutritional conditions (from the Institute of Animal Physiology, Babraham, Cambridge). A third set of radiographs was taken at 3 month intervals over a single year on living Soay sheep kept under good conditions at the Rowett Research Institute, Aberdeen. Measurements were taken on the radiographs of length, minimum shaft width (SW) and medullary cavity width (MCW), while combined cortical thickness (CCT) was calculated. The ewes from Hirta had significantly lower values for CCT than those from Babraham, whereas the rams showed no significant reduction in CCT. Since no seasonal variation in CCT was detected in the well nourished Rowett ewes, this indicates a differential effect of poor environmental conditions on bone metabolism in ewes. It is proposed here that this may be related to the additional stress imposed by gestation and lactation on female animals living under conditions of seasonally restricted food supply.