A randomized, controlled clinical trial investigated the effect of early enteral nutrition (EN) on intestinal permeability, intestinal protein loss, and outcome in parvoviral enteritis. Dogs were randomized into 2 groups: 15 dogs received no food until vomiting had ceased for 12 hours (mean 50 hours after admission; NPO group), and 15 dogs received early EN by nasoesophageal tube from 12 hours after admission (EEN group). All other treatments were identical. Intestinal permeability was assessed by 6-hour urinary lactulose (L) and rhamnose (R) recoveries (%L, %R) and L/R recovery ratios. Intestinal protein loss was quantified by fecal α1-proteinase inhibitor concentrations (α1-PI). Median time to normalization of demeanor, appetite, vomiting, and diarrhea was 1 day shorter for the EEN group for each variable. Body weight increased insignificantly from admission in the NPO group (day 3: 2.5±2.8% day 6: 4.3±2.3% mean ± SE), whereas the EEN group exhibited significant weight gain (day 3: 8.1±2.7% day 6: 9.7 ± 2.1%). Mean urinary %L was increased, %R reduced, and L/R recovery ratios increased compared to reference values throughout the study for both groups. Percent lactulose recovery decreased in the EEN group (admission: 22.6±8.0% day 6: 17.9 ± 2.3%) and increased in the NPO group (admission: 11.0±2.6% day 6: 22.5 ± 4.6%, P= .035). Fecal α1-PI was above reference values in both groups and declined progressively. No significant differences occurred for %R, L/R ratios, or α1-PI between groups. Thirteen NPO dogs and all EEN dogs survived (P= .48). The EEN group showed earlier clinical improvement and significant weight gain. The significantly decreased %L in the EEN versus NPO group might reflect improved gut barrier function, which could limit bacterial or endotoxin translocation.