The microbiota of ensiled forages and of bulk tank milk on dairy cattle farms in northern Sweden - a case study

Factors contributing to variations in the quality and microbiota of ensiled forages and in bulk tank microbiota in milk from cows fed different forages were investigated. Nutritional quality, fermentation parameters and hygiene quality of forage samples and corresponding bulk tank milk samples collected in 3 periods from 18 commercial farms located in northern Sweden were compared. Principal coordinates analysis revealed that the microbiota in forage and bulk milk, analyzed using 16S rRNA gene-based amplicon sequencing, were significantly different. The genera Lactobacillus, Weissella and Leuconostoc dominated in forage samples, whereas Pseudomonas, Staphylococcus and Streptococcus dominated in bulk milk samples. Forage quality and forage-associated microbiota were affected by ensiling method and by use of silage additive. Forages stored in bunker and tower silos (confounded with use of additive) were associated with higher levels of acetic and lactic acid and Lactobacillus. Forage ensiled as bales (confounded with no use of additive) was associated with higher dry matter content, water-soluble carbohydrate content, pH, yeast count and the genera Weissella, Leuconostoc and Enterococcus. For bulk tank milk samples, milking system was identified as the major factor affecting the microbiota and type of forage preservation had little impact. Analysis of common amplicon sequence variants (ASVs) suggested that forage was not the major source of Lactobacillus found in bulk tank milk.