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. Therefore, our results indicate that feeding the higher starter CP content is not a viable strategy to compensate for the negative effects of SBO supplementation on the growth performance of dairy calves.
