Selective Dry-Off Therapy in Conventional Dairy Farms: The Influence of Quarter-Level Selection Criteria on Postpartum Mastitis and Somatic Cell Count

The present study assessed the efficacy of selective dry cow therapy (SDCT) on two commercial Holstein-Friesian farms in the Czech Republic, involving 572 quarter milk samples from 74 cows collected over a two-year period. Quarter samples were taken both at dry-off (n = 296) and post-calving (n = 276) to assess somatic cell count (SCC), cultured microbial results (counts), milk composition, and mastitis incidence. The average SCC at dry-off was 264,000 cells/mL (SD = 650,000) in Farm 1 and 224,000 cells/mL in Farm 2. Mastitis incidence averaged 24.42% and 18.75% in Farms 1 and 2, respectively. Correlation analysis revealed significant associations between pre-dry-off milk parameters and post-calving udder health indicators, including negative correlations between SCC prior to drying-off and lactose content after calving (r = -0.161, <i>p</i> < 0.01). Statistical analyses showed a significant farm effect on cultured microbial occurrence and mastitis occurrence after calving (<i>p</i> < 0.05), as well as a significant influence of lactation number on postpartum mastitis and SCC (<i>p</i> < 0.05). Also, mastitis incidence was significantly higher (9.43%, <i>p</i> < 0.05) in treated quarters. The use of selective non-antibiotic dry cow therapy does not impair udder health and milk quality but helps reduce the risk of antibiotic resistance. Further refinement of diagnostic criteria is needed to optimize treatment decisions and improve herd-level outcomes.