Dietary Live Yeast Supplementation Influence on Cow's Milk, Teat and Bedding Microbiota in a Grass-Diet Dairy System.

The supplementation of animal feed with microbial additives remains questioning for the traditional or quality label raw milk cheeses with regard to microbial transfer to milk. We evaluated the effect of dietary administration of live yeast on performance and microbiota of raw milk, teat skin, and bedding material of dairy cows. Two balanced groups of cows (21 primiparous 114 ± 24 DIM, 18 multiparous 115 ± 33 DIM) received either a concentrate supplemented with Saccharomyces cerevisiae CNCM I-1077 (1 × 1010 CFU/d) during four months (LY group) or no live yeast (C group). The microbiota in individual milk samples, teat skins, and bedding material were analysed using culture dependent techniques and high-throughput amplicon sequencing. The live yeast supplementation showed a numerical increase on body weight over the experiment and there was a tendency for higher milk yield for LY group. A sequence with 100% identity to that of the live yeast was sporadically found in fungal amplicon datasets of teat skin and bedding material but never detected in milk samples. The bedding material and teat skin from LY group presented a higher abundance of Pichia kudriavzevii reaching 53% (p < 0.05) and 10% (p < 0.05) respectively. A significant proportion of bacterial and fungal ASVs shared between the teat skin and the milk of the corresponding individual was highlighted.

Cow teat skin, a potential source of diverse microbial populations for cheese production.

The diversity of the microbial community on cow teat skin was evaluated using a culture-dependent method based on the use of different dairy-specific media, followed by the identification of isolates by 16S rRNA gene sequencing. This was combined with a direct molecular approach by cloning and 16S rRNA gene sequencing. This study highlighted the large diversity of the bacterial community that may be found on teat skin, where 79.8% of clones corresponded to various unidentified species as well as 66 identified species, mainly belonging to those commonly found in raw milk (Enterococcus, Pediococcus, Enterobacter, Pantoea, Aerococcus, and Staphylococcus). Several of them, such as nonstarter lactic acid bacteria (NSLAB), Staphylococcus, and Actinobacteria, may contribute to the development of the sensory characteristics of cheese during ripening. Therefore, teat skin could be an interesting source or vector of biodiversity for milk. Variations of microbial counts and diversity between the farms studied have been observed. Moreover, Staphylococcus auricularis, Staphylococcus devriesei, Staphylococcus arlettae, Streptococcus bovis, Streptococcus equinus, Clavibacter michiganensis, Coprococcus catus, or Arthrobacter gandavensis commensal bacteria of teat skin and teat canal, as well as human skin, are not common in milk, suggesting that there is a breakdown of microbial flow from animal to milk. It would then be interesting to thoroughly study this microbial flow from teat to milk.

Do milking practices influence the bacterial diversity of raw milk?

The link between milk production practices and bacterial diversity of 67 raw milks from dairy farms in the Savoie and Haute-Savoie regions of France was studied by Single Strand Conformation Polymorphism (SSCP) analysis. The milking practices and the cleanliness of different parts of the cow housing were evaluated. The SSCP bacterial profiles allow to classify the 67 milks into three groups: group A was characterised by a majority of Gram-positive non-lactic acid bacteria (Corynebacterineae and Micrococcaceae) and a high level of hygiene in milking practices. The SSCP profiles of groups B and C were close but different from those of group A: they were both dominated by lactic acid bacteria and by a less intensive hygiene practices. The group B milks were characterised by the dominance of Gram-negative bacteria and Lactococcus lactis species while those of group C were dominated by Brevibacterium linens and Leuconostoc mesenteroides. The variation of balance between bacterial populations can be associated with differences in hygienic milking production practices.