The aim of this study was to investigate the effect of two different levels of starter protein and amounts of milk fed on animal health, fecal score, immune responses and microbial population in the rumen of Holstein male calves. Two levels of starter crude protein (17 and 20% of starter dry matter (DM) and two levels of milk fed (7 and 10% of body weight) were combined in a 2 × 2 factorial exp...