Single oral dose of bovine Fc-fused single-domain antibody enables multi-week serum detectability in neonatal calves.

Neonatal calf diarrhea caused by bovine rotavirus (BRV) remains a major health and economic burden in cattle production, and current oral antibody approaches require frequent dosing because of poor systemic persistence. This study investigated whether a single oral dose of a BRV-specific antibody engineered with an immunoglobulin Fc region-designed to extend circulatory half-life-could be detected in the blood of newborn calves for up to 28 days. The antibody construct showed high-affinity binding to BRV antigen and effectively neutralized viral infection in cell culture. In a controlled calf trial, neonatal Holstein calves under 24 h of age (n = 5 per group) received a single oral dose of 20 mg of the Fc-fused antibody in milk replacer; control calves received milk replacer alone. Blood samples were collected over 28 days. Treated calves showed numerically higher serum antibody signals than controls throughout the observation period, with statistically significant differences at days 6 and 10. An assay targeting the Fc region provided numerically greater group separation than a general antibody detection format. These results provide proof-of-principle that a single oral dose of an Fc-fused single-domain antibody was systemically detectable for up to 28 days in neonatal calves, supporting the potential for extended dosing intervals compared with conventional oral immunoglobulin strategies.