The udder microbiota in dairy cows: importance for animal health and welfare, mastitis and milk quality

The healthy bovine udder produces high quality milk and is the starting point for quality milk products. Milk from the udder may also be a source of types of lactic acid bacteria that are used for the production of fermented dairy products. Until recently, the healthy udder has been considered to contain only small numbers of insignificant microorganisms but it has now been shown that a complex microbiota is present inside the udder, and can potentially protect the udder from infection. Mastitis is an infection of the udder caused mainly by bacteria and which causes pain and distress to the cow and considerable losses of milk and profit. Antimicrobial medication generally effects a cure for mastitis but unfortunately disturbs not only the microbiota in the udder but also in other parts of the body. There is international focus on reduction of the use of antimicrobials due to the emergence of resistant microorganisms. Research on the udder microbiota in health and disease is therefore needed. Milk production systems in Norway differ to other countries in several respects and studying the udder microbiota in Norwegian cows is therefore important for milk production and the dairy industry in Norway. In the Jurfrisk project, two main studies have been conducted to investigate the composition and temporal changes of the udder microbiota in the Norwegian red breed. In the first study, over 400 samples of milk from udders were analyzed to establish which bacteria taxa dominate the microbiota in healthy lactating cows. Two main bacterial families have been identified to be present in all the cows. These two families, Corynebacteriaceae and Staphylococcaceae, have been previously reported in other mammalian microbiomes such as epithelium and nasal and they might be considered part of the resilient microbiota. In addition, the study of the udder microbiota highlighted a high incidence of quarter dysbiosis, alteration of the healthy microbial composition, in healthy cows. These results were published in Scientific Reports journal. Changes in udder microbial composition showed that the quarters of healthy cows are also subjected to temporal perturbations of its microbiota composition. During a six-month period, the udder microbiota showed changes in the amount and types of potential pathogenic taxa, such as Staphylococcaceae and Streptococcaceae. These dynamic changes were significantly different based on the cow and the somatic cell count. An article has been published in Animal Microbiome journal. Antibiotic treatment remains one of the most used methods to fight clinical mastitis. These mastitis treatments comprise about 50 to 60 % of the total antibiotic usage within the dairy industry. It is important to understand that antibiotic treatment will disturb the resident microbiota and that this in itself will likely reduce the resistance of the udder to a new infection. To investigate how a possible antibiotic treatment might impact the microbiota in the udder, a novel approach was used. Milk samples collected from the previous two samplings were inoculated in sterilized milk containing the two most used antibiotics in the dairy industry (Penicillin G and Aoxicillin/clauvic acid) to investigate which members of the milk microbiota were able to survive and dominate inside the udder. Amplicon sequencing and isolation of microbes with subsequent minimal inhibition concentration test showed that antibiotic resistant species were similar to the one usually found the bovine udder. This indicates that antibiotic treatments for mastitis perturbate the natural microbiota by reducing its diversity and by selecting antibiotic resistant bacteria which become the dominant taxa in the udder.

New scientific knowledge has been uncovered with regards to the composition of the bovine udder microbiota. Results from the project point to the importance of the udder microbiome in the health and disease of the dairy cow. Identification of the core microbiota showed that taxa adapted to the udder environment have the possibility to persist over a long period and that this core microbiota is diverse between quarters, farm location and period of the year. In addition, a highly diverse udder microbiota might be implicated in the protection of the udder from new bacterial species that might otherwise develop to mastitis. This result can be exploited as a support tool for decision regarding the handling of mastitis. Mapping the udder microbiota at cow level would provide better knowledge on the possibility of a more precise monitoring of mastitis. More precise monitoring of mastitis is important in forming treatment recommendations by the dairy industry to farmers and the continuation of selective breeding against mastitis and high cell counts. Furthermore, better monitoring of mastitis benefits animal health, diagnostics, veterinary care and improved application of antimicrobials (targeted antimicrobial treatment). The study of antibiotic resistance among the udder microbiota provided knowledge of which microbial species are potentially able to survive the treatment currently used in the dairy farming system. At the same time, this provides insights to what extent the microbiota balance is destroyed by antimicrobial treatment. With this knowledge and novel method for quickly identify mastitis pathogens (such as Nanopore sequencing), treatments of mastitis can be performed with a higher precision toward bacteria which are not resistant to antibiotics. This will reduce the overall usage of antimicrobials in dairy farming. Metabolism and milk quality during growth of selected lactic acid bacteria and mastitis pathogens showed diverse mechanisms used to grow in milk. This gave insights into how these microorganisms contribute to changes in the milk whilst in the udder. Development of methods for detection of metabolites and biomarkers produced by LAB and mastitis pathogens could be exploited to obtain quick identification of problematic animals with reduce milk quality and presence of subclinical mastitis. Future works on microbe-microbe interactions and microbe-host interactions are of great interest to identify mechanisms of defense and pathogenicity within the bovine udder and during mastitis.

Mastitis is a production-limiting and economically important inflammatory disease of the bovine udder and generally has an infectious origin. The healthy udder, previously regarded to contain only small numbers of insignificant microorganisms, has in recent reports been shown to have its own microbiota, which might have a role in protecting the udder from infections. Antibiotics generally cure mastitis but will also detrimentally affect the microbiota of not only the udder and also elsewhere in the body. As part of the international drive to reduce the use of antibiotics, in order to slow down the development of resistant microorganisms, research on the udder microbiota in health and disease is needed. The udder microbiota is underresearched and more knowledge is needed to understand how the natural microbiota has a role against mastitic infections. Milk production systems in Norway differ to other countries and studying the effect on udder microbiota is important for the Norwegian dairy industry. This research project is a collaboration between NMBU, both at Ås and Adamstuen. The microbiota of the udder of cows from two dairy herds will be analysed and correlated to factors such as different anatomical locations in the udder, previous medical history, lactation time and previous antibiotic treatment. The microbiota in healthy cows and those with clinical and sub-clinical mastitis will be compared, using the very latest molecular techniques. This will provide new insights into the udder microbiota. Selected strains of lactic acid bacteria isolated from udder samples, will be investigated for their metabolism in milk and compared to strains used in dairy fermentations. The microbiota results will also be compared with some international studies, where different animal husbandry is practiced. In addition, links to the milk and animal health research environment at SLU, Sweden and PhD mobility will be encouraged. This will increase the impact of the research.