Omics & gene networks

Intramammary challenge with mastitis pathogens elicits specific blood transcriptome profile indicating targeted systemic response

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Abstract

Mastitis is a major concern in dairy cattle production with strong impact on animal health and welfare and thus, breeding for lower susceptibility to mastitis is a breeding goal in all major dairy cattle breeding programs. A variety of microbial pathogens can elicit a substantially divergent clinical outcome ranging from strictly local infection of the mammary gland to life-threatening systemic response depending on the invading pathogen and the immune response of the host. Infections with S. aureus are mostly assumed to be restricted to a local inflammation and to take a chronic disease outcome. However, previously we had described a distinct hepatic transcriptome response. On the other hand, E. coli infections usually take a much more severe clinical course with substantially impaired animal welfare indicating a systemic scenario. The objective our study was to monitor the systemic response of first-lactation dairy heifers after intra-mammary challenge with S. aureus or E. coli. For the experiment, 36 early lactation half-sib heifers were recruited, which had been selected for divergent susceptibility to mastitis according to genomic prediction and had inherited alternative paternal BTA18 haplotypes. At day 36 +/- 3 post partum, the heifers were inoculated with a S. aureus (n=24) or E.coli (n=12) strain, which had been isolated from clinical mastitis cases. The animals were closely monitored for their clinical phenotype across the entire experiment and intermediate blood samples were collected from immediately before inoculation until euthanasia at 24 h (E. coli) or 96 h (S. aureus) after infection. Blood samples were processed for global transcriptome analysis. Taking a threshold of at least four samples with an FPKM threshold of 0.1, we found a total 17.430 loci expressed in the whole blood transcriptome. Comparing the transcriptome signature before the pathogen inoculation and the status at the endpoint of the experiment, we detected distinct differences between both pathogens. This applied to the magnitude of differentially expressed genes (padj < 0.05 S. aureus-challenge 1,949 loci, E. coli challenge 5,858 loci) as well as to the most strongly differentially expressed genes themselves. The rather strong signal to pathogen inoculation for the S.aureus group confirmed the previously described hepatic response of the same animals and indicates a systemic signaling also for this pathogen, although S.aureus is usually assumed to elicit only a local inflammation. For E. coli, the differentially expressed genes demonstrated a massive activation of the innate immune system 24 h after intramammary challenge, which is also in line with the previously described hepatic transcriptome profile of the heifers. The data from the in-vivo inoculation experiment demonstrate the substantially different response pattern to both pathogens, which might suggest to consider a pathogen-associated genetic susceptibility for improving udder health in dairy cattle breeding.

Keywords: 2026

How to Cite:

Becker, D., Heimes, A., Meyerholz-Wohllebe, M., Petzl, W., Engelmann, S., Schuberth, J., Zerbe, H., Hoedemaker, M. & Kühn, C., (2026) “Intramammary challenge with mastitis pathogens elicits specific blood transcriptome profile indicating targeted systemic response”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2286768. doi: https://doi.org/10.31274/wcgalp.24114

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