Efficacy of lime-based conditioner against environmental udder pathogens in different bedding materials

Bedding type and management influence bacterial growth, potentially increasing the risk of new intramammary infections (IMI) in dairy cows. We investigated the effect of various concentrations of lime-based conditioner (LBC) on four environmental udder pathogens (<i>Escherichia coli, Klebsiella pneumoniae, Enterococcus faecium,</i> and <i>Streptococcus uberis</i>) inoculated into new sand, recycled manure solids (RMS), and sawdust. Bedding substrates were collected from commercial dairy farms, sterilized, and separately inoculated with bacterial suspensions. Increasing concentrations of LBC (0 %, 10 %, 15 %, and 20 %) were applied and samples were incubated for 24, 72, and 168 h at 28 °C to assess growth dynamics, dry matter content (DM), and pH. LBC increased the pH of all bedding materials. In sand and RMS, pH levels rose substantially, reaching 12.83 ± 0.05 and 11.72 ± 0.12, respectively. In sawdust the pH increase was lower, reaching 10.91 ± 0.14 with 20 % LBC. Sand showed inherent resistance to bacterial growth, with 10 % LBC completely inhibiting bacterial proliferation. Untreated RMS readily supported bacterial growth and required high LBC concentrations. In RMS, LBC controlled <i>E. coli</i> and <i>K. pneumoniae</i> better than <i>S. uberis</i> and <i>E. faecium.</i> Sawdust required LBC concentrations of 20 % to effectively control <i>E. coli and K. pneumoniae</i> growth<i>. E. faecium</i> was generally unaffected by LBC, while <i>S. uberis</i> growth was inhibited in sawdust even without LBC addition. LBC was therefore successful in reducing mastitis pathogen loads, with an effectiveness depending on concentration and substrate type. Future research on practical on-farm applications will be required to validate these findings.