Evaluating case definitions of respiratory disease in dairy calves: a scoping review

Bovine respiratory disease (BRD) is one of the most common diseases observed in dairy calves in both the pre- and post-weaning periods. Despite its common occurrence, there has been no formal synthesis (e.g., scoping review) of the scientific literature surrounding diagnosing BRD in dairy calves. As such, the objective of this scoping review was to describe what case definitions for diagnosing BRD in dairy calves have been used in research. An initial search of peer-reviewed journals and the gray literature yielded 12,001 unique articles, of which 307 records containing 358 case definitions were included. Seven categories of diagnostic methods were used to categorize case definitions: (1) clinical scoring systems alone were the most used diagnostic method (n = 148, 41%) followed by (4) physical exam parameters alone (i.e., the study did not provide a detailed description of how the calf was assessed for each component of the physical exam [i.e., no description or scoring options reported]), n = 91, 25%), (5) physical exam parameters in combination with other diagnostic methods (n = 40, 11%), (6) thoracic ultrasound alone (n = 31, 9%), (2) clinical scoring system in combination with other diagnostic methods (n = 23, 7%), (3) clinical scoring system in combination with thoracic ultrasound (n = 10, 3%), and (7) other diagnostic methods (n = 15, 4%). Only 2-thirds of publications provided a citation for their case definition (n = 230, 64%), of which the Wisconsin clinical scoring system was most referenced (n = 100, 43%), followed by the California clinical scoring system (n = 19, 8%). An attempt was made to compare entire case definitions within each diagnostic method; however, they displayed substantial diversity which limited the ability to compare them at this level. Instead, counts of individual factors within each case definition (e.g., individual clinical signs) were reported for each diagnostic method. From all case definitions across the 7 diagnostic method categories (n = 358), common factors assessed included cough (n = 224, 63%), nasal discharge (n = 213, 60%), and body temperature (n = 142, 54%). Across all case definitions, additional parameters such as validity were frequently not reported – only 4 (1.1%) were referred to as validated, 9 (2.5%) were being validated in the study, and 28 (7.8%) modified existing case definitions. Additionally, assessment of severity of disease when present (e.g., mild, moderate or severe) was frequently not report