In order to investigate the effect of physical form of starter and hay on dairy Holstein calves performance, 52 males of Holstein dairy calves were used in a completely randomized design. Dietary treatments were: 1) ground (G), 2) texturized (steam flake corn and steam flake barley (,) T), 3) pellet (P) and 4) ground+10 % forage (GF). All calves were weaned at d 50.All diets were formulated to be isoenergetic and isonitrogenous. Rumen fluid samples were collected via a stomach tube at d 35 and 70 of the study. 12 calves were slaughtered at d 70. The starter intake and Average daily gain (ADG) were influenced by the treatments at pre weaning ( P 0.05), post weaning and the whole trail ( P 0.0001). Also, starter intake and ADG for calves use GF was highest. There were no differences in feed efficiency among treatments during pre-weaning and post weaning. But, there were significant difference in feed efficiency between treatments at the whole trail ( P = 0.01).Final and weaning weight were affected by the treatments at weaning ( P = 0.01) and trail end ( P 0.0001). Final and weaning weights for calves fed with GF were highest. Body measurements such as hip width, hip height, body length, wither height and heart girth were not significantly different among the treatments during pre-weaning and post weaning .The stomach size was influenced by the treatments at pre weaning ( P = 0.01), and post weaning ( P 0.01). Stomach size for calves fed with GF was highest. VFA and Ammonia-N concentration were influenced by the treatments ( P = 0.01) at post weaning. Ruminal pH was influenced by the treatments ( P 0.0001) at post weaning and ruminal pH was highest for the calves fed the GF diet. dry and organic matter digestibility at pre weaning and post weaning, and crud pr digestibility at post weaning were influenced by the treatments ( P 0.01), and these were lowest for the calves fed the G diet. The thickness of the epithelial( P = 0.05), Length and circular muscles layer thickness, the total thickness of the muscles, the total thickness of the wall, and creatine layers, Papillae length and Papillae width were influenced by the treatments ( P 0.01). The thickness of the epithelial and creatine layer and Papillae width were lowest for the calves fed the GF diet. In conclusion, the result indicated that adding forage along with concentrate improved performance and rumen development of dairy Holstein calves. Keywords: Holstein Calf -Starter diets- Forage- Papillae- Rumen development
