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

## TL;DR

This study shows that selective dry cow therapy can reduce antibiotic use in dairy farming without harming udder health or milk quality, provided proper selection criteria are used.

## Contribution

The study provides empirical evidence supporting the effectiveness of selective dry cow therapy in reducing antibiotic use while maintaining udder health in dairy cows.

## Key findings

- Quarters treated with antibiotics had higher clinical mastitis incidence, likely due to pre-existing infections.
- Selective dry cow therapy did not impair udder health or milk quality when appropriate selection criteria were applied.
- There was a significant farm effect on microbial occurrence and mastitis after calving.

## Abstract

This study evaluated the use of selective dry cow therapy in two commercial dairy farms in the Czech Republic to reduce antibiotic use without harming udder health or milk quality. Milk quarter samples were collected before and after drying-off to analyze somatic cell counts, microbial infections, and milk composition. The results showed no significant differences in udder health between quarters treated with or without antibiotics when appropriate selection criteria were applied. However, quarters treated with antibiotics tended to have a higher clinical mastitis incidence, likely due to pre-existing infections. These findings support the use of selective dry cow therapy as a sustainable approach to lower antibiotic use in dairy farming while maintaining animal welfare and milk quality. Improved diagnostic methods and careful herd management are essential for successful implementation.

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, p < 0.01). Statistical analyses showed a significant farm effect on cultured microbial occurrence and mastitis occurrence after calving (p < 0.05), as well as a significant influence of lactation number on postpartum mastitis and SCC (p < 0.05). Also, mastitis incidence was significantly higher (9.43%, p < 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.