Relationship Between Subclinical Mastitis Occurrence and Pathogen Prevalence in Two Different Automatic Milking Systems

This study compared two types of automatic milking systems (AMSs) and their relationship with epidemiological indices of subclinical mastitis (SCM) and prevalence of mastitis-causing pathogens. Conducted between 2020 and 2023 on a dairy farm in Vacaria, Rio Grande do Sul, Brazil, this study analyzed data from 464 lactating cows housed in compost-bedded pack barns (CBPBs) and milked by eight AMS units: four from DeLaval (which utilizes teat cup for teat cleaning) and four from Lely (which utilizes brushes for teat cleaning). SCM incidence, prevalence, percentage of chronic, and cured cows were determined using somatic cell counts (SCCs) and microbiological cultures. Statistical analyses included the Wilcoxon signed-rank test and Chi-square test to evaluate SCM indices and pathogen associations with AMSs. No significant difference was observed in SCM prevalence (<i>p</i> = 0.3371), percentage of chronic (<i>p</i> = 0.3590) and cured cows (<i>p</i> = 0.4038), SCC (<i>p</i> = 0.1290), and total bacterial count (TBC) (<i>p</i> = 0.8750) between AMS types. However, the SCM incidence was higher in the Lely (14.7%) than in the DeLaval AMS (9.1%) (<i>p</i> = 0.0032). The Chi-square results revealed that the Lely AMS was associated with major pathogens like <i>Staphylococcus aureus</i> and <i>Escherichia coli</i>, whereas DeLaval showed associations with minor environmental and contagious pathogens, particularly non-aureus <i>Staphylococci</i>. The findings indicate a relationship between AMS-cleaning systems and pathogen spread, suggesting that Lely AMS may contribute to more aggressive infections due to its cleaning system.