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 are 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.