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Background <p>Post-milking teat spraying plays an important role in the control of mastitis within New Zealand dairy herds. We examined the sample-level associations between post-milking teat spraying and bacterial levels in bulk tank milk (BTM) microbiomes, using shotgun DNA sequencing data within a non-experimental framework.</p> Methods <p>A total of 1325 BTM samples were collected from 219 pasture-based commercial herds voluntarily enrolled across New Zealand, over the 2021 and 2022 dairy seasons. Bacterial levels of <i>Staphylococcus</i> and <i>Streptococcus</i> species and <i>Corynebacterium bovis</i> were quantified (cells/ml) and compared along with two post-milking teat spray actives (iodine and chlorhexidine) and two application methods (manual and automatic). Analyses were performed at the BTM sample level using log-transformed abundances and the Wilcoxon rank-sum test; Benjamini–Hochberg FDR was applied per individual species. A univariate PERMANOVA (Euclidean distance, 9,999 permutations) was used as a permutation-based robustness check.</p> Results <p>These data show that post-milking teat spraying was associated with lower BTM levels of <i>Corynebacterium bovis</i> and lower levels across <i>Staphylococcus</i> species compared with samples without teat disinfection, across both seasons. At the teat spray active level, Chlorhexidine-based teat disinfectant was associated with lower <i>Corynebacterium bovis</i>, <i>Staphylococcus aureus</i>, and <i>Streptococcus dysgalactiae</i> than the iodine-based teat disinfectant, while no consistent differences were observed for <i>Streptococcus uberis</i>,<i> Streptococcus agalactiae</i>,<i> Streptococcus chromogenes</i>, or <i>Streptococcus epidermidis</i>. For the teat spray application method, patterns varied by species. Findings were consistent across two seasons and directionally consistent between Wilcoxon and PERMANOVA.</p> Conclusions <p>We demonstrate that sequencing-based BTM microbiome profiling can reveal sample-level associations between teat spray practices and mastitis-associated bacteria. While causal inference is constrained by the observational design and uncertain sources contribution within BTM, these findings suggest that BTM sequencing may complement herd-level monitoring of teat spray performance. Further controlled studies incorporating key covariates are warranted.</p>

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Using sequence-derived microbiome information from bulk tank milk samples to assess the influence of post-milking teat disinfection in New Zealand dairy herds

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月6日

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  • Hong Ling,
  • John Williamson,
  • Sean Gatenby,
  • Seren Pruden,
  • Catherine Neeley,
  • Chad Harland,
  • Andrew Wallace,
  • Christine Couldrey

摘要

Background

Post-milking teat spraying plays an important role in the control of mastitis within New Zealand dairy herds. We examined the sample-level associations between post-milking teat spraying and bacterial levels in bulk tank milk (BTM) microbiomes, using shotgun DNA sequencing data within a non-experimental framework.

Methods

A total of 1325 BTM samples were collected from 219 pasture-based commercial herds voluntarily enrolled across New Zealand, over the 2021 and 2022 dairy seasons. Bacterial levels of Staphylococcus and Streptococcus species and Corynebacterium bovis were quantified (cells/ml) and compared along with two post-milking teat spray actives (iodine and chlorhexidine) and two application methods (manual and automatic). Analyses were performed at the BTM sample level using log-transformed abundances and the Wilcoxon rank-sum test; Benjamini–Hochberg FDR was applied per individual species. A univariate PERMANOVA (Euclidean distance, 9,999 permutations) was used as a permutation-based robustness check.

Results

These data show that post-milking teat spraying was associated with lower BTM levels of Corynebacterium bovis and lower levels across Staphylococcus species compared with samples without teat disinfection, across both seasons. At the teat spray active level, Chlorhexidine-based teat disinfectant was associated with lower Corynebacterium bovis, Staphylococcus aureus, and Streptococcus dysgalactiae than the iodine-based teat disinfectant, while no consistent differences were observed for Streptococcus uberis, Streptococcus agalactiae, Streptococcus chromogenes, or Streptococcus epidermidis. For the teat spray application method, patterns varied by species. Findings were consistent across two seasons and directionally consistent between Wilcoxon and PERMANOVA.

Conclusions

We demonstrate that sequencing-based BTM microbiome profiling can reveal sample-level associations between teat spray practices and mastitis-associated bacteria. While causal inference is constrained by the observational design and uncertain sources contribution within BTM, these findings suggest that BTM sequencing may complement herd-level monitoring of teat spray performance. Further controlled studies incorporating key covariates are warranted.