Bovine respiratory disease (BRD) is an important disease of
calves that leads to reduced weight gain and productivity
(Waltner-Toews et al., 1986; Warnick et al., 1997; Donovan
et al., 1998). Field diagnosis remains a challenge for control
and treatment of BRD. Several clinical scoring systems have
been proposed, including the Wisconsin (WI) system
(McGuirk, 2008) that uses five clinical signs, each partitioned
into four levels of severity. Recently, we developed a BRD scoring
system for pre-weaned dairy calves based on a matched case–control
study of 2030 Holstein calves on a large calf ranch in the San
Joaquin Valley, California (CA) (BRD3 scoring system; Love et al.,
2014). The CA BRD scoring system is based on the presence or
absence of six clinical signs, each assigned a model-based score
(Appendix 1). The objective of this study was to estimate the