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Abstract Background The milk microflora is closely associated with the physiology and pathology of the mammary gland, and plays a pivotal role in the development of offspring. The aim of this study was to examine the variability of milk microflora diversity in relation to seasonal, herd-specific, subclinical mastitis status, and parity-related effects. Results Milk samples were collected from 285 cows in Ningxia, China, followed by the exploration of microflora using 16S rRNA pyrosequencing. Subsequently, all samples were categorized based on seasonal variations (summer and winter), cow health status (healthy and subclinical mastitis cows), farm origins (6 commercial dairy farms), and parity levels (primiparity and multiparity). The bacterial diversity, community composition, and abundance were assessed in distinct cohorts. Additionally, the milk microflora from samples collected during summer, winter, and colostrum was compared. The findings indicated a significant variation in the bacterial diversity of milk between samples collected from summer and winter. It was observed that the summer samples exhibited higher bacterial richness compared to the winter samples. The gut-related genera, including Parabacteroides, Staphylococcus, Corynebacterium₁, Sphingomonas, and Lactobacillus, were found to be prevalent in milk samples collected in summer. Conversely, EscherichiaShigella, Pseudomonas, Streptococcus, Psychrobacter, Rhizobium, Bifidobacterium, and Clostridiumₛensuₛtricto₁ were commonly observed in winter samples. The subclinical mastitis cows showed a significantly higher alpha diversity value (chao1 and Shannon index) compared to the healthy cows (summer). Sporolactobacillus, Mycobacterium, EscherichiaShigella, and Actionmycetaceae were identified as biomarkers in the subclinical mastitis cows. In addition, the top 20 KEGG pathways were significantly reduced in the subclinical mastitis group compared to the healthy cows in summer, particularly in membrane transport, cell motility, and signal transduction pathways. The bacterial diversity varied across different farms, with Farms A and B demonstrating a higher degree of similarity of milk bacterial composition, while Farms D and F also displayed similarities. Farm C appeared distinct from other farms. Furthermore, there was observed a greater bacterial richness in multiparous cows compared to primiparous cows. Additionally, the comparative analysis revealed a significant difference in alpha and beta diversity, bacterial profiles among summer, winter and colostrum samples. Conclusions The study indicated that the composition of milk microflora exhibited variability across different seasons, farms, healthy status, and parities. Furthermore, distinct microflora characteristics were observed in milk samples obtained during summer, winter, and colostrum stages.
Xie Xiu-lan (Tue,) studied this question.