Disease dynamics and antimicrobial use in pre-weaned Holstein calves paired at different ages

Social housing of dairy calves has been proposed as an alternative to individual housing to improve calf welfare; but their effects on health remain inconsistent. This study evaluated the association among pairing age, occurrence of diarrhea and bovine respiratory disease (BRD), as well as antimicrobial use, during the preweaning period. The study was conducted on a commercial farm in Paraná, Brazil, using 140 Holstein calves assigned to pair housing at 7, 30, or 50 days of age. Calves were monitored daily until weaning using the Wisconsin Calf Health Scoring System, and treatments were recorded. Diarrhea was more frequent than BRD, with fever predominantly associated with BRD. Pairing age did not affect the odds, severity, or timing of diarrhea or BRD, nor the likelihood of both calves within a pair being affected, or the interval between cases. Overall antimicrobial use did not differ among pairing ages; however, calves paired later required less antimicrobial use for diarrhea than early or intermediate calves. Survival analysis confirmed no effect of pairing age on the probability of remaining disease-free. These findings indicate that pair housing at different ages does not compromise calf health, but may influence the diarrhea cases with fever and the antimicrobial use for diarrhea.