There is a growing interest in using whole grains as a potential alternative to forage in starter feed due to their adequate particle size and potential prevention of forage’s negative effects in starter feed. This could improve dairy calves’ feed intake and performance. Therefore, to determine the optimum level of whole corn grain in starter feed on feed intake, performance, health, ruminal fermentation, and blood metabolites of dairy calves, forty-eight Holstein calves [4-day-old; 41.10 ± 2.56 kg of body weight (BW), 12 per treatment] were randomly assigned to each of the following four treatments: 1) starter feed contained corn grain as ground with no whole corn grain (WC0); 2) starter feed where 33% of ground corn was replaced with whole corn grain (WC33); 3) starter feed where 66% of ground corn was replaced with whole corn grain (WC66); and 4) starter feed where 100% of ground corn was replaced with whole corn grain (WC100). For the purpose of gathering post-weaning data, the calves were weaned on day 60 and left until day 74. The experimental treatments had no significant effect on BW, but the starter feed and total dry matter intake (TDMI) tended (P = 0.051) to respond cubically with increasing WC inclusion. Throughout the entire period, the wither height tended (P = 0.09) to increase linearly as WC increased in starter feed. The fecal score, respiratory score and days with diarrhea did not differ between treatments. Throughout the research, calves fed the WC0 diet had lower (P = 0.01) rumen pH levels compared with the other treatments, and rumen acetate concentrations decreased (P = 0.02) cubically and acetate-to-propionate ratio tended (P = 0.07) to increase linearly in calves consuming WC. There were no differences in blood metabolites among the experimental groups during the overall period. Given the observed rumen fermentation modulations under the conditions of the current experiment, we concluded that grinding all the corn grain in forage-free starter feeds is not recommended for dairy calves. Feed intake-related data indicated that partial replacement (33%) of ground with whole corn could lead to greater intake.
