Urea is the major contributor to nonprotein nitrogen fraction of milk which represents 5 to 6% of the total nitrogen in milk. Milk urea (MU) nitrogen is closely related to blood urea nitrogen which is derived from at least two sources: the liver detoxification of ammonia diffused from the rumen and the amino acid catabolism in the liver (Depeters and Ferguson, 1992). Thereby, MU concentration could reflect the protein metabolism in the cow and be related to the diet. Several studies showed significant links between MU concentration and nutritional variables (mostly dietary crude protein and energy:protein ratio) or environmental factors (e.g. season or stage of lactation) (Broderick and Clayton, 1997; Schepers and Meijer, 1998; Godden et al., 2000). MU has proved to be an interesting management tool for breeders (Jonker et al., 2001). The aim of our research is to provide feed management tools to Walloon dairy farmers based on the detection of ‘abnormal’ values. To develop such a tool, MU concentrations need to be predicted for future test days. Given the nature of MU, this presents a special challenge and this study will show first results obtained when testing two different models.