A Longitudinal Observation Study to Investigate the Associations Between Individual Qualitative Behavioural Assessment Scores and Milk Production in Housed Dairy Cows in the UK.

Qualitative Behavioural Assessment (QBA) has been used at both the herd and individual levels as an indirect measure to assess changes in the emotional state in dairy cattle but has not been used in individual cattle to explore associations between emotional state and milk production over a lactation. The study assessed 114 individual cows over a 13-month period utilising QBA and milk production data on a single farm. QBA scores were analysed using Principal Component Analysis (PCA). A decrease in Principal Component 1 (PC1) was associated with an increase in scores for positive behavioural terms such as happy, relaxed, calm and content. An increase in Principal Component 2 (PC2) was associated with an increased score for terms such as active, playful and inquisitive. Analysis with mixed models showed that milk yield was significantly negatively associated with PC1 for first-lactation cows (estimate = -0.24, p = 0.016) whilst accounting for days in milk (DIM) and temporal dependence. Variations in daily milk yields, assessed using the log-transformed variance of deviations from individual lactation curves (LnVar), were significantly positively associated with PC1 (percentage change in variability = 3.63, p = 0.004). These results indicate that increased milk yield and reduced daily yield variation were associated with more positive behavioural QBA terms. Exploratory work using clustering of PCA scores from the first 30 DIM was associated with 100-day milk yield, with cows in the more positive clusters (cluster 2 for PC1 and cluster 2 for PC2) producing the greater yield volumes (PC1 cluster 2: estimate 529.4, p = 0.02; PC2 cluster 2: estimate 1158.5, p < 0.001). These findings suggest that cows with more positive emotion scores are associated with increased milk production and provides evidence for further exploration in this research area.