Abstract
BackgroundSand is often considered the preferred bedding material for dairy cows as it is thought to have lower bacterial counts than organic bedding materials and cows bedded on sand experience fewer cases of lameness and disease. Sand can also be efficiently recycled and reused, making it cost-effective. However, some studies have suggested that the residual organic material present in recycled sand can serve as a reservoir for commensal and pathogenic bacteria, although no studies have yet characterized the total bacterial community composition. Here we sought to characterize the bacterial community composition of a Wisconsin dairy farm bedding sand recycling system and its dynamics across several stages of the recycling process during both summer and winter using 16S rRNA gene amplicon sequencing.ResultsBacterial community compositions of the sand recycling system differed by both seasons and stage. Summer samples had higher richness and distinct community compositions, relative to winter samples. In both summer and winter samples, the diversity of recycled sand decreased with time drying in the recycling room. Compositionally, summer sand 14 d post-recycling was enriched in operational taxonomic units (OTUs) belonging to the genera Acinetobacter and Pseudomonas, relative to freshly washed sand and sand from cow pens. In contrast, no OTUs were found to be enriched in winter sand. The sand recycling system contained an overall core microbiota of 141 OTUs representing 68.45% ± 10.33% SD of the total bacterial relative abundance at each sampled stage. The 4 most abundant genera in this core microbiota included Acinetobacter, Psychrobacter, Corynebacterium, and Pseudomonas. Acinetobacter was present in greater abundance in summer samples, whereas Psychrobacter and Corynebacterium had higher relative abundances in winter samples. Pseudomonas had consistent relative abundances across both seasons.ConclusionsThese findings highlight the potential of recycled bedding sand as a bacterial reservoir that warrants further study.
Highlights
Sand is often considered the preferred bedding material for dairy cows as it is thought to have lower bacterial counts than organic bedding materials and cows bedded on sand experience fewer cases of lameness and disease
Sampling and sequencing summary A total of 1,833,757 raw sequences were generated from 26 summer samples (947,496 sequences), 18 winter samples (884,245 sequences), and 4 polymerase chain reaction (PCR) negative controls (2,016 sequences)
Members of the core microbiota we identified accounted for a surprisingly large portion of the bacterial community relative abundance for all locations, which suggests a large portion of the recycled sand microbiota may be stable and consistent across seasons
Summary
Sand is often considered the preferred bedding material for dairy cows as it is thought to have lower bacterial counts than organic bedding materials and cows bedded on sand experience fewer cases of lameness and disease. Sand is separated from organic material, cleaned with a disinfectant, and left to dry in the recycling room This method typically leads to a sand recovery rate of > 90% and several studies have shown recycled sand to have no significant difference in bacterial load, relative to clean sand [8, 13, 14]. These results contrast with a more recent survey of 169 U.S dairy herds, which found unused recycled bedding sand to have increased total bacterial counts when compared to unused fresh sand [11]. It has been suggested that recycled bedding sand could serve as a potential reservoir for bacterial pathogens [11, 15]
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