From dry-off to early lactation : longitudinal assessment of metabolic disorders and resilience in dairy cows milked in automated milking systems

This thesis investigates the physiological manifestation of prevalent metabolic disorders and systemic inflammation in cows milked in automated milking systems (AMS). As AMS adoption expands globally, promoting higher milking frequencies and milk production, understanding cow health and resilience in these systems is critical. Current diagnostic thresholds for subclinical hypocalcemia (SCH) and hyperketonemia (HYK) are largely derived from tie-stall or conventional free-stall herds, and their applicability to modern AMS herds remains uncertain. This research followed 400 multiparous cows across two commercial AMS herds in British Columbia, Canada. Cows were enrolled at dry-off and monitored through 60 days in milk (DIM) to characterize SCH and HYK patterns, evaluate associations with production, behavior, and inflammation, and identify potential biomarkers of resilience. Patterns of SCH were comparable to conventional herds, with calcium at 1 and 4 DIM strongly associated with milk yield. Monitoring to 6 DIM revealed additional variation: cows that remained hypocalcemic produced less milk, spent less time eating prepartum, and exhibited elevated inflammation during early lactation. Analysis of HYK events using blood beta-hydroxy butyrate concentrations (BHB > 1.2 mmol/L) during the first 14 DIM showed that persistent HYK, defined as consecutive HYK events, occurred primarily in high-producing cows despite reduced feed intake and rumination around calving. Cows with fluctuating HYK (isolated HYK events) did not differ from negative HYK cows in health, behavior, or production outcomes, suggesting that elevated BHB may be a natural consequence of increased milk production. Examination of resiliency phenotypes using inflammation profiles, measured via serum amyloid A from dry-off to 14 DIM, combined with production outcomes across 60 DIM, revealed distinct patterns. Cows with high inflammation and low production were most vulnerable, exhibiting the highest number of health events, reduced feeding time in the first week, and lower calcium at 4 and 6 DIM. In contrast, cows with low inflammation and high production displayed a resilient phenotype, with stable rumination and eating behavior, low incidence of health events, and sustained calcium concentrations. Collectively, these findings advance understanding of metabolic disorders, inflammation, and behavior in AMS herds, guiding detection, intervention, and management strategies to improve cow health and productivity.