Nauta et al., 2006b; Fall, 2009). The results of the present study show large differences between the production systems regarding the proportion of cows culled due to poor udder health, contrary to the results of Hamilton et al. (2006), who found a similar rate of culling due to mastitis in a small study of Swedish organic and conventional herds. Our results agree with results by Rozzi et al. (2007) who showed that in Canadian organic herds, mastitis and fertility are the most common reasons for culling. However, whereas mastitis and fertility are equally common reasons for culling in Canada, the main reason for culling in Swedish organic herds is poor udder health. Contrary results are probably due to differences in organic standards, conditionsfor conventional production, trait definition, and methods of analysis. In the present study, a large proportion of the cows (19% of the Swedish Holstein and 16% of the Swedish Red cows) had no specified cause of culling. However, we do not believe that farmers’ use of the code “unspecified cause” is connected to any specific reason for culling. The use of this code is therefore not likely to affect the results.