Negatively controlled trial investigating the effect of dry cow therapy in first-lactation dairy cows on the prevalence of intramammary infections in the subsequent lactation.

Summary

This randomised controlled trial in 446 first-lactation dairy cows evaluated whether dry cow therapy (DCT) could be safely withheld in well-managed herds. Withholding intramammary antibiotics whilst retaining internal teat sealant increased early postpartum prevalence of gram-positive pathogens, particularly non-aureus Staphylococci and Mammaliicocci (RR 1.95), suggesting that selective DCT guided by milk quality indicators may be necessary even in well-managed farms. The findings provide data to inform antibiotic stewardship strategies whilst maintaining udder health.

Regional applicability

This study was conducted in a United States dairy herd with high management standards. The findings on selective dry cow therapy strategies are relevant to United Kingdom dairy producers seeking to optimise antibiotic use whilst maintaining udder health, though farm-specific prevalence of pathogens and management conditions may differ and should be considered when adapting selective DCT protocols.

Key measures

Quarter-level intramammary infection prevalence (postpartum milk culture results); somatic cell count (SCC) and California mastitis test (CMT) results at dry-off; relative risk of gram-positive pathogen infection; antibiotic use prediction

Outcomes reported

The study assessed the impact of withholding dry cow therapy (antibiotics and internal teat sealant) on quarter-level intramammary infection prevalence in the postpartum period, and evaluated how selective therapy guided by somatic cell count and California mastitis test could predict antibiotic use and udder health outcomes. Primary outcome measured was postpartum IMI prevalence; secondary outcomes included IMI prevalence stratified by baseline milk quality indicators.

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