Expression of selected cytokine genes in healthy dairy cow udder quarters adjacent to quarters subclinically infected with staphylococci

Introduction This study evaluated how subclinical staphylococcal infection in one quarter influences cytokine expression in adjacent healthy quarters, exploring inter-quarter signalling. Material and Methods Fifty udder quarters were sampled from 50 Polish Holstein-Friesian cows. Quarters were categorised as infected with coagulase-positive (CoPS) or coagulase-negative (CoNS) staphylococci, adjacent healthy quarters (AHCoPS or AHCoNS), and entirely healthy controls (H). Expression of 11 cytokines was analysed using RT-qPCR and ELISA. Results Samples of AHCoPS showed lower mRNA levels of IL1A , IL1B , IL2 , IL6 , IL12A , IL12B , TNF and CXCL5 genes compared with AHCoNS and were similar to samples of H. Samples of AHCoNS showed higher mRNA levels of nearly all genes compared with samples of H. Moreover, AHCoNS samples showed higher IL-1β, IL-6 and IL-18 protein levels than both CoNS and H samples. Notably, lower IL-6 and IL-18 concentrations were seen in AHCoPS than in CoPS tissue. Conclusion Subclinical staphylococcal mastitis in one quarter modulates immune responses in adjacent quarters, disrupting local homeostasis. The results reveal that the bovine udder functions as an integrated, complex organ rather than four independent glands, which has practical implications for mastitis management and milk quality assessment.