Increasing the particle size of starter by changing the particle size of straw at a 5% inclusion rate resulted in minimal changes in ruminal fermentation, no effect on fecal particle size, pH, and starch content, and no change in rumen development parameters. The size of the omasum decreased as particle size increased; the implications of this change may be beneficial to the calf and need to be elucidated. Under the conditions of this study, increasing the particle size of low-quality forage to calf diets did not improve rumen development parameters or provided with a more stable rumen fermentation