Colostrum somatic cell counts and their association with the bacterial microbiota at udder quarter level in Simmental cows

Analysing the somatic cell count (SCC) together with the microbiota composition in colostrum can be useful for monitoring udder health immediately after parturition. The present study aimed to explore the bacterial community in colostrum of Simmental cows, and to assess whether the bacterial diversity and composition related to the SCC at the udder quarter level. The SCC were examined in colostrum and milk on days 14 and 28 postpartum, which were aseptically collected separately for each udder quarter from 16 cows. The SCC was determined immediately after milking. The DNA was extracted from defatted colostrum and used for 16S rRNA amplicon sequencing. Results showed higher SCC in colostrum than in milk on day 14 and 28 postpartum. Colostrum was predominated by environmental bacteria (e.g., Delftia and Cutibacterium). Season did not affect SCC but colostrum collected in summer months contained more Delftia, whereas Methylobacterium-Methylorubrum and Acinetobacter were more abundant in the fall. Quarters on the left body side tended to have higher SCC and increased species richness than the quarters on the right body side. Partial least squares-discriminant analysis indicated that colostrum samples with low SCC (< 100 × 10³ cells/mL) were characterized by high abundances of Lactobacillus and Cutibacterium, whereas Methylobacterium-Methylorubrum discriminated for colostrum with high SCC. Colostrum samples with high SCC (> 1000 × 10³ cells/mL) also tended to contain more Streptococcus. Pearson correlations supported a link between higher SCC on day 28 and abundance of Streptococcus and Bacillus in colostrum, which should be further exploited in the future.

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