The aim of the project is to develop tools which can be used for individually adapted lactation lengths based on the biological conditions of the cow. Today a one year calving interval and a short lactation period, is recommended. The recommendations are based on 30 years old information and do not take into account individual variations between cows. In this project 20 large dairy herds will be included. We will gain information from the individual cows in each herd related to milk yield, fertility and health and validate the tools as predictors of cows which benefit from an extended lactation. We will test the tools by selecting primiparous cows based on the developed predictive tools. We will create genomic breeding values which can be used to identify cows which benefit for an extended lactation. We envision that farmers who adopt the concept of individually adapted lactation lengths will experience better health and welfare, fertility and productivity in their herds.