Positive Emotional States in Dairy Cows: Reflections in Milk Quality and Udder Health.

Integrating positive welfare indicators into dairy science is gaining attention, yet the biological correlates of affective states in commercial herds remain poorly understood. This study explored associations between dairy cows' emotional states quantified through the Positive Affect Index (PAI) derived from the Qualitative Behaviour (QBA) Assessment and milk biomarkers, yield, and udder health indicators across 37 commercial farms. Descriptive statistics, housing-adjusted linear regressions, and partial Spearman correlations were used to explore these relationships. Higher PAI values, indicating more positive herd-level emotional states, were significantly associated with lower SCC (22% reduction, p = 0.016) and lower odds of elevated DSCC (OR = 0.69, p = 0.002), reflecting improved udder health. Positive affect was also linked to a higher lactose concentration (p < 0.001) and an increased fat-to-protein ratio (FPR). A tendency for higher milk yield (+1.07 L per milking, p = 0.077) and slightly lower protein content was observed, consistent with a dilution effect. These associations remained robust after sensitivity analyses and were independent of housing type. The results demonstrate that milk composition and udder health biologically reflect positive emotional states, supporting the integration of behavioural assessments and milk biomarkers as a non-invasive framework for advancing welfare-oriented and precision dairy farming.