Does a forage feeding regime of heifers during the milk feeding period show any carry over effects? Does hay fed during this period give calves any disadvantages or advantages, which are even visible after switching them to a single diet? Can any differences in the rumen development be found? Should hay really be restricted during the pre weaning period like many researchers suggest? This paper is based on an experiment, which was made with the same calves that Khan et al. (2011) used for his study, trying to answer the questions mentioned above. On week 12 of live, they were switched to a single diet with access to ad libi-tum hay and only restricted starter. In comparison were feed intake, nutrients con-sumption, body weight, growth parameters and blood ?-hydroxybutyrate value with and without previous access to hay.