Evaluating clinical mastitis in four dimensions: Part I. Defining the production, immunological, clinical and pathogen severity

Assessing the severity of clinical mastitis (CM) is a critical step in making treatment decisions and plays a crucial role in mastitis control and ensuring animal welfare. The prevailing method for assessing the severity of CM mainly considers clinical symptoms. However, the severity of CM can be assessed from various perspectives. This study aims to define and assess CM severity in four dimensions: production, immunology, clinic, and pathogen. We collected data on naturally occurring CM cases on three robotic dairy farms in Belgium (N = 2) and the Netherlands (N = 1), involving four types of information: quarter-level milk yield, cow-level somatic cell count (SCC), clinical symptoms, and causative pathogens. The final dataset for analysis included 129 CM cases detected by the herdsmen from 105 cows and 113 lactations. In the production dimension, CM severity was defined based on the maximum relative quarter-level milk loss for the clinically inflamed and clinically uninflamed quarters separately. In the immunological dimension, severity was defined based on the deviation of the cow-level SCC from a cow-level baseline. The clinical dimension used existing scoring and stratified between mild, moderate and severe cases. Finally, the severity in the pathogen dimension was based on the bacteriological culture results of a milk sample collected from the inflamed quarter on the detection day. For each dimension, scores between farms, parities, and lactation stages (LS) were compared. A significant difference was only found between farms, both in the production and clinical dimension. Combining the four scores may help to capture the full scope of CM by simultaneously assessing the severity of cases across production, immunological, clinical, and pathogen-related dimensions.