Changes in Antimicrobial Component Concentrations at the Onset of the Dry Period and Peripartum in Dairy Cows

We aimed to clarify antimicrobial component (AMC) dynamics during the dry period in dairy cows and determine the impacts of varying somatic cell count (SCC) at the onset of the dry period on the subsequent changes in AMC concentrations in milk. Milk samples obtained from Holstein dairy cows were categorized into low-SCC and high-SCC groups. AMC concentrations in milk were measured at four time points: (1) Onset of the dry period, (2) before calving, (3) immediately after calving, and (4) 1 week postpartum. In the low-SCC group, SCC and lingual antimicrobial peptide increased prepartum but decreased 1 week postpartum. Milk lactoperoxidase and lactoferrin concentrations increased prepartum but declined after calving, while cathelicidin-7, S100A7, and S100A8 concentrations increased after calving compared to those prepartum in both groups. S100A7 concentrations in the low-SCC group were significantly higher than those in the high-SCC group prepartum and immediately after calving. However, S100A8 concentrations in the low-SCC group were significantly lower than those in the high-SCC group prepartum and 1 week postpartum. These results suggest that some AMCs were elevated after the onset of the dry period and immediately after calving and highlight the importance of mitigating inflammation in the mammary glands before the onset of the dry period.