Changes in survival of cattle (Bos taurus) during Medieval times in two Norwegian cities

Bones (diaphyses) have epiphyses that fuse at a given age. This indicates if the animal was older or younger than the age of fusion for that specific epiphysis at death. In this short contribution, we present a new methodology to calculate survival/mortality of cattle on the basis of epiphysial fusion. We used cattle bones, excavated in two Norwegian cities, Oslo and Trondheim, to calculate survival and changes in mortality for cattle during the period from AD1000 to AD1624. This is based on standard logistic regression models, using a complementary log–log link and the log of age of fusion of the epiphyses as independent variable, an approach recognised as a ‘Weibull-model for current-status-data’. Mortality of cattle was higher in the city of Trondheim than in Oslo. For both cities the mortality of cattle decreased, and the life-span increased, during the period from the AD1000 until AD1350. In Oslo, mortality after 1350 was similar to that between 1150 and 1250, while in Trondheim, it was similar to the mortality in the period from 1250 to 1350. We have shown that mortality curves can be calculated using epiphysial fusion data, and using this approach have demonstrated a change in cattle mortality which corresponds to significant historic events during the medieval period.