<p>This study evaluated the effects of forage source (alfalfa hay, AH; vs. wheat straw, WS) and delivery method (mixed, MIX; vs. separate, SP) on growth performance, health, nutrient digestibility, rumen fermentation, and blood metabolites in Holstein dairy calves. Forty-eight heifer calves were assigned from d 4 to 79 of age to four treatments based on finely ground calf starters offered either separately or mixed with AH or WS: SP-AH, SP-WS, MIX-AH, and MIX-WS. Forage source and delivery method did not affect body weight (BW) or feed efficiency (FE). During the pre-weaning period, SP calves tended to have greater total dry matter intake (TDMI), starter, and neutral detergent fiber (NDF) intake, with the highest forage intake in SP-AH calves. Post-weaning, WS calves exhibited greater average daily gain (ADG), TDMI, starter, and NDF intake than AH calves. Overall, SP increased forage intake, whereas WS tended to increase TDMI, starter, and NDF intake. AH increased nutrient digestibility on day 72 and body length, and SP-AH calves had greater hip width at weaning. SP tended to reduce post-weaning diarrhea days, whereas WS calves required more medical treatments. WS feeding increased eating and ruminating time and reduced lying time across the study. Post-weaning, MIX calves had higher total volatile fatty acid (VFA) and acetate concentrations, and tended toward lower ruminal pH. Post-weaning, WS calves had higher blood glucose, while AH calves tended to have higher blood urea nitrogen. In conclusion, forage source and delivery method differentially influenced intake, digestibility, rumen fermentation, health, and selected growth responses of dairy calves in a stage-dependent manner.</p>