Are microbiomes important to mammary gland health in dairy cows?

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Mastitis, caused by a wide range of bacteria, is the most economically important endemic disease of dairy cows. Intramammary infections (IMI) result in ~1 in 6 cows dying/being culled per year, reducing food production efficiency and food security. Recent studies have shown there are microbiomes in the gut, mouth, skin and human mammary gland (MG). We propose to define the MG microbiome, its dynamics and relationship with changing intramammary health and disease leading to a paradigm shift in our understanding of IMI. We will test the following hypotheses:

There is a functional microbiome in the bovine MG which develops from birth
The MG microbiome has a direct role in bovine MG health
Pathogens in the MG do not always cause disease, due in part to the microbiome
Deeper culturing from milk than the current standard will improve IMI management

We will analyse mammary tissue of ~30 immature cows and foetuses using culture and molecular techniques described below to show when bacteria begin to colonise the MG.

In a prospective, longitudinal study we will collect 12 repeat samples from 800 quarters (giving quarter sample sets) from 200 cows on 2 farms from drying off to 4 weeks post calving. We will select at least 65 quarter sample sets where IMI occurred and 65 uninfected sets for analysis. We will use qPCR to estimate total bacterial load and pyrosequencing to identify members of the microbiome. We will model these data to investigate how the microbiome forms and changes over time at drying off, with calving, milking, mastitis and antibiotic treatment. We will determine whether specific bacteria or combinations of bacteria help protect against mastitis, how antibiotics impact disease management and control and produce ideas for new strategies to develop and maintain health and milk output and quality. We will use enhanced culture of 20% of the above samples to test whether industry could refine its current standards to improve treatment/prevention of IMI.

Endemic and chronic bacterial diseases are a major health and welfare issue for both humans and animals and many appear to be associated with the disturbance of naturally existing microbiomes. In our project, we aim to understand the role the bovine mammary gland microbiome plays in intramammary infections (IMI) in dairy cattle and gain insights into its pathogenesis and management. IMI have major economic, environmental and welfare impacts. Therefore the results from this project have potential to impact across a number of animal (cattle, sheep and pig) and also human sectors, from fundamental and applied science to the actual management of mammary gland health on farms. The 'Pathways to Impact' of this proposal describes how end-users and other stakeholders will be engaged.

Understanding chronic bacterial diseases.
If our hypotheses prove to be correct and the MG is similar to other epithelial sites (which seems reasonable) then our results will have a direct impact on the dairy industry (vets, agricultural advisors and farmers), the veterinary pharmaceutical companies and all parties interested in diseases where the causative bacteria live in communities e.g. bacterial causes of lameness, abortion, pneumonia, dental disease, urogenital disease, gut diseases for example.

Current management of intramammary infections
This project will provide evidence that explains how the current management of IMI perturbs the MG microbiome and challenges the current approach that one pathogen causes disease in an otherwise 'sterile' udder. Current management and strategies for prevention of IMI may have to be reviewed. Our immediate message might appear negative; that current strategies for management and prevention will not lead to a significant reduction in the incidence of IMI. However, this knowledge will have a positive impact, because new management and treatment strategies should be possible and our results will open the way for new approaches to improve the prevention of IMI. Particular attention will be paid to possible novel treatments should the data suggest these may be possible and suitable partners within the ARC (Dairy Co, pharmaceutical companies) will be sought to exploit these ideas.

Our project will produce results that will help define how microbiomes function within individuals and how microbiomes respond to perturbations. In addition we will develop statistical models incorporating microbiome, host and environmental data. Such data and concepts will be directly relevant to organisations seeking to understand and exploit microbiomes or microbial communities in other environments, including humans and engineered systems. KJP has an ongoing collaboration with researchers investigating wound biofilm development and its treatment, which represents a similar poly-microbial environment.

This project, while based in the strategic science of understanding and controlling IMI, has the potential to impact both fundamental and strategic science across many fields. It will provide a model for investigating, understanding and potentially exploiting microbiomes and in the use of cutting-edge scientific approaches to tackling real-world problems in a coherent multidisciplinary fashion.