This study investigated the effects of feeding dairy calves starter diets containing 19% or 22% crude protein (CP) content on dry matter (DM) basis and either supplemented or not with soybean oil (SBO, 0 vs. 3%, DM basis) on growth performance, digestibility, urinary nitrogen, and purine derivatives (PD) excretion. A total of 48 female Holstein dairy calves (mean 39.8 kg body weight) were randomly distributed to experimental diets in a 2 × 2 factorial arrangement of treatments. The four dietary treatments were 1) starter diet without SBO supplement and 19% CP (NSBO-19CP), 2) starter diet without SBO supplement and 22% CP (NSBO-22CP), 3) starter diet with 3% SBO and 19% CP (SBO-19CP), and 4) starter diet with 3% SBO and 22% CP (SBO-22CP). Milk feeding value was similarly based on a constant protocol across experimental treatments and calves had ad libitum access to water and starter diets throughout the study. All calves were weaned on d 63 of age and remained in the study until d 83 of age. Calves supplemented with SBO had lower starter feed intake and average daily gain (ADG) and lower feed efficiency (FE) but had a higher fecal score indicating a higher likelihood of diarrhea occurrence compared with unsupplemented calves. Wither heights, digestibilities of organic matter, CP, and neutral detergent fiber (NDF) were decreased, and ruminal volatile fatty acids tended to be reduced, and the molar proportion of ruminal butyrate (preweaning) and acetate (postweaning) reduced by supplemental SBO. The urinary allantoin and total PD excretion were reduced; however, urinary nitrogen excretion was increased when calves were supplemented with SBO. The CP amount did not affect starter feed intake, FE, or diarrhea occurrence rate, whereas 22CP diets increased neutral detergent fiber digestibility, improved ADG (tendency), and increased allantoin and urinary PD excretion compared to 19CP diets. The starter feed intake, ADG, FE, diarrhea occurrence rate, nutrient digestibility,
