Associations between vacuum-, milk flow-, and teat-based milking parameters and somatic cell count

The primary objective of this study was to evaluate the relationship between milk flow-based parameters, vacuum-based milking variables, and teat health and morphology metrics in relation to both quarter- and cow-level SCC across lactation. Data were collected from 58 cows during 1 wk/mo over an 8-mo period (April to November 2024). Multivariable mixed models were used to identify factors significantly associated with quarter- and cow-level log₁₀-transformed SCC (log₁₀SCC). This study demonstrates associations between vacuum-, milk flow-, and teat-based milking parameters and SCC at both levels of analysis. Mouthpiece chamber (MPC) vacuum during the total milking period was positively associated with log₁₀SCC at both the quarter and cow levels. Increasing severity of teat-end hyperkeratosis was also associated with higher log₁₀SCC at both levels. At the quarter level, low average milk flow, high peak milk flow, longer dead time, and wider teat diameter were associated with increased log₁₀SCC, whereas at the cow level, shorter high-flow duration showed this association. Together, these findings highlight multiple relationships among machine settings, milk flow dynamics, and teat condition in determining udder health outcomes. Although this study cannot establish causation because of its observational design, and is intended to describe within-system relationships under controlled milking conditions rather than evidence of universal or population-level effects, the results support the value of monitoring of MPC vacuum, assessing milk flow characteristics, and routinely evaluating teat condition when interpreting SCC patterns in dairy herd.