Association of Somatic Cell Score at First Calving With Milk Productivity and Mortality in Dairy Herds: A Cross-Sectional Study in Eastern Hokkaido, Japan

Over the past decade, the increasing proportion of primiparous cows in Hokkaido dairy herds has resulted in younger herds, but somatic cell count (SCC) has stagnated at around 220,000 cells/mL, preventing milk quality improvements. This study evaluated the impact of elevated postpartum somatic cell scores (SCS) in primiparous cows on herd productivity, aiming to inform milk quality improvement measures in Hokkaido. Production data from 163 herds in Eastern Hokkaido were analyzed, with milk yield per cow, herd SCC, and mortality used as dependent variables and primiparous cow SCS as the independent variable. Results revealed a significant positive association between primiparous cow SCS and both herd SCC and mortality, whereas a significant negative association was observed with milk yield per cow. These findings suggest that high SCS in primiparous cows may reflect suboptimal animal welfare practices, such as poor udder hygiene and inadequate peripartum management. Enhancing welfare practices, such as udder hygiene, and providing a supportive calving environment could improve SCS in primiparous cows, increase milk productivity, and reduce mortality. Additionally, supporting farmers by using SCC levels of primiparous cows as a benchmark could be an effective strategy for improving milk quality in the Hokkaido region.