Temperament influences productivity, health, and welfare in dairy cattle, and the autonomic nervous system (ANS), along with its serotonergic pathways, may represent a key link between behavioral and physiological traits. This study investigated the relationships among serotonin (5-hydroxytryptamine; 5-HT), the startle response (i.e., an ANS-regulated reflexive reaction to a sudden stimulus), productivity, behavior, and physiology in dairy cows managed in an automatic milking system (AMS). Lactating Holstein cows (n = 24) were observed over a 46-day period, and AMS-derived variables collected included dead milk time (DMT; s/visit), energy-corrected milk (ECM; kg/d), milk speed (MS; kg/min), milk yield (MY; kg/d), milk variability, fat:protein ratio (FPR), refusals (count/d), and rumination minutes (RUM; min/d). Drinking behaviors, namely, drinking bouts (Bouts; count/d), milk:water, water:milk, and water intake (WI; L/d), were recorded across the same 46-day period using a commercially available bolus. A startle test was performed when the same cohort of cows reached the dry period, and behavioral reactions, namely, defecation (count), freeze-like state, jump, post-startle magnitude-activity (PSM-A), post-startle magnitude-inactivity (PSM-I), and startle magnitude (SM), were quantified. Blood samples were collected independently from the startle test for serum 5-HT analysis. Mixed models in SAS (9.4) were used to evaluate the relationships among SM, 5-HT, production, drinking, and behavioral measures. Regression analyses were performed on key relationships, and Spearman correlations and factor analyses identified associations and latent dimensions among key variables. Startle magnitude was positively associated with MY (P = 0.02) and ECM (P = 0.05) and negatively associated with refusals (P < 0.01). Startle magnitude tended to correlate positively with MY (P = 0.07) and milk:water (P = 0.08) and negatively with WI (P = 0.05). Moreover, 5-HT concentration tended to be positively correlated with SM (P = 0.08) and negatively with freeze-like state (P < 0.01). Factor analysis identified three latent factors explaining 52.26% of the variance: 1) resource efficiency and physiology (DMT, jump, milk:water, neutrophil lymphocyte, SM, and 5-HT), 2) AMS behavior and temperament (DMT, defecation, RUM, freeze-like state, and PSM-A), and 3) milking dynamics and ANS (DMT, FPR, MS, neutrophil:lymphocyte, and jump). These findings suggest that serotonergic activity and startle responsivity may synergistically characterize multiple physiological and behavioral dimensions of temperament relevant to dairy cow welfare and productivity. Integrating behavioral and neurophysiological measures could improve the assessment of resilience and coping ability in precision dairy systems.
Ceja et al. (Wed,) studied this question.