Overfeeding with a high-concentrate diet activates the NOD1-NF-κB signalling pathway in the mammary gland of mid-lactating dairy cows.

Long term high-concentrate (HC) diet feeding induces subacute ruminal acidosis (SARA), which is reported to trigger a pro-inflammatory response. This study aimed to investigate the role of nucleotide-binding oligomerization domain protein 1 (NOD1) in initiating the pro-inflammatory response triggered by grain-induced SARA in the mammary gland of mid-lactating dairy cows. Twelve multiparous mid-lactating Holstein cows (455 ± 28 kg) were randomly assigned into two groups to conduct the experiment for 18 weeks as follows: one group was fed a low-concentrate (LC) diet as a control (40% grain), and the other was fed an HC diet as a treatment (60% grain). Overall, the results showed that a decreased rumen pH and elevated γ-D-glutamyl-meso-diaminopimelic acid (iE-DAP) concentrations in the HC group compared with LC group. The concentration of pro-inflammatory cytokines, including interleukin (IL)-1β, IL-6 and tumour necrosis factor-alpha (TNF-α), significantly increased in the lacteal vein of the HC group than LC group. The mRNA expression levels of NOD1, receptor-interacting protein2 (RIP2), NF-κBp65 (p65), IL-1β, IL-6, IL-8 and TNF-α, which involved in inflammatory response, were up-regulated in the HC-induced mammary gland. The changes of the target proteins, including NOD1, p65 and pp65 presented the same tendency as those of the target genes. Collectively, long-term high concentrate feeding-induced SARA increased the rumen iE-DAP concentration which activated NOD1-NF-κB signalling pathway-dependent inflammation in the mammary gland of mid-lactating cows.