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Associations Between Bovine Respiratory Disease Complex and the Probability and Latency of Group- Reared Neonatal Dairy Calves to Approach a Novel Object or Stationary Person
Bovine respiratory disease complex (BRD) is an important disease that impacts the welfare and performance of dairy calves. With group housing of calves becoming more common, it is imperative to identify behaviors indicative of illness in a socially competitive environment. The objective of this study was to determine associations between BRD status of group housed dairy calves and their latency to approach a novel object or stationary person. On a commercial dairy in Wisconsin, 75 Holstein preweaned group housed heifer calves were tested once a week for 6 weeks. The average age of calves upon enrollment was 4.1 ± 1.9 days. Calves were housed in eight pens with an average of 9 ± 1 calves per pen. Each week, all calves in the study were tested for their willingness to approach a novel object (OBJ) and a stationary person (SP) within 60 seconds. Approach was defined as one step in the direction of SP or OBJ. Pen and test order were randomized. After both OBJ and SP tests were complete, a standardized health assessment was conducted. The behaviors of calves with clinical signs of BRD were compared to calves with no clinical signs of BRD. All models were controlled for week, pen, pen order, and test order. Associations between probability of approach and BRD status were analyzed using a linear mixed model with a logit transform (PROC GLIMMIX), controlling for calf as a random effect. Calves without BRD were 2.5 [95% CL: 1.4 to 4.6] and 2.6 times [95% CL: 1.4 to 4.8] as likely to approach than calves without BRD for the SP (P < 0.005) and OBJ tests (P<0.005), respectively. The latency of calves that approached the SP or OBJ was analyzed using a Cox proportional hazards regression (PROC PHREG). BRD status did not significantly impact the latency to approach in either test. The median latency to approach was 18 seconds and 9 seconds for SP and OBJ tests, respectively. Clinical signs of BRD impacted the probability of approach but did not impact the latency to approach, which indicates that BRD influences the willingness to approach but not the rapidity at which a calf approaches. These findings suggest that approach tests may be used to identify calves with BRD in group housing.
Keywords: Behavior, BRD, Calves