Respiratory disease adversely affects preweaned dairy calves in the short and long term, contributing to morbidity and mortality, decreased growth and loss in milk production, according to recent research published in the Journal of Dairy Science.

Approximately 12% of calves in the U.S. are treated for respiratory disease, most commonly presenting as bronchopneumonia. Systemic antibiotic therapy is the most common treatment for calves with this diagnosis. In an article appearing in the Journal of Dairy Science, scientists from the University of Wisconsin-Madison and Michigan State University assessed the effects of early antibiotic therapy on preweaned calves diagnosed with respiratory disease using respiratory scoring and portable lung ultrasound.

Researchers examined calves from two herds in southern Wisconsin twice per week from three to five days of age until weaning at approximately 56 days. The examination included a clinical respiratory examination, lung ultrasound, fecal score and heart girth measurement. For diagnosis, a positive case was determined with a combination of a calf’s clinical respiratory score and its lung ultrasound score.

“Although our method of diagnosis is not considered a gold standard, it likely represents the closest, most practical way that we have at the moment to characterize consequential lung disease in dairy calves,” said lead author Dr. Theresa Ollivett with the department of medical sciences in the University of Wisconsin-Madison School of Veterinary Medicine.

Of the 357 calves enrolled in the study, 289 calves developed respiratory disease. Calves that tested positive for respiratory disease were randomly assigned to receive either an antibiotic labeled to treat respiratory disease or a placebo with an equal amount of saline solution at first detection, an announcement said.

“In theory, the earlier in the pathologic process that therapeutic drug levels are achieved within the parenchyma of the lung, the faster bacterial replication and neutrophil infiltration should cease, stifling the progression of lung lesions and hastening the resolution of lung consolidation,” Ollivett said.

Antibiotic therapy with one dose of a long-acting macrolide delayed the progression of lung consolidation and re-treatment, reduced mortality and increased growth.

“We hope this study will stimulate more thought and research on how antimicrobial stewardship is addressed and, further, will help to quantify treatment success of antibiotic protocols on farms and in research settings,” Ollivett said.

The study indicated short-term benefits of early antibiotic therapy after diagnosis via respiratory scoring and lung ultrasound. Overall, however, lung consolidation recurred and persisted to weaning, despite early diagnosis and treatment, and the authors called for more research to address antimicrobial stewardship and treatments in on-farm and research settings.