Toaff-Rosenstein, R. L., Tucker, C. B. 2018. The sickness response at and before clinical diagnosis of spontaneous bovine respiratory disease. Applied Animal Behaviour Science 201, 85-92.

Bovine respiratory disease (BRD) is often diagnosed in feedlots after observing behavioral changes such as anorexia, with fever confirmatory. However, this method has poor diagnostic accuracy compared to postmortem lung lesions. Little is known about how these or other sickness responses such as low grooming present in early, spontaneous BRD, especially during feedlot acclimation. To inform improved detection, we studied 3 aspects of the BRD sickness response at and before diagnosis and the effect of acclimation on behavior in beef heifers. We hypothesized that heifers with BRD would have fever and spend less time feeding and grooming compared to controls, and that both behaviors would increase with acclimation. Beef heifers were randomized to replicate and pen, balanced for body weight (total n = 80), and monitored for 12 d, starting 2 d after shipping. Rectal temperature was measured with a logger, while feeding time and brush use were video-recorded. Clinical signs were recorded daily: heifers remaining healthy over the entire 12 d were Controls (n = 46); those meeting set criteria were classified as BRD (n = 21). Health effects were analyzed for all 3 dependent variables on the day of diagnosis (d 0), and for fever and feeding, the 2 days before (d −1 and −2), using analogous days for Controls. Acclimation effects were tested separately using all available behavioral data. BRD heifers had a fever on d 0 and −2 (≥0.4 °C higher than Control, P < 0.01) but not on d −1 (P = 0.10). After excluding 4 outliers (all Controls; never seen at the feed bunk), BRD heifers had lower feeding time on d 0 (19% less than Control, P = 0.04), but not on d −1 or −2 (P ≥ 0.32); or at all when outliers were included (P ≥ 0.32). BRD had no effect on brush use (29.6 ± 6.6 vs. 19.8 ± 4.4 min/18.5 h; P = 0.22). While feeding behavior was stable over time (P = 0.28), the effect of outliers suggests that acclimation may also affect anorexia-based diagnosis of individual heifers. Brush use results also reflect the effect of acclimation to a novel device, evidenced by generally increased grooming later compared to earlier days (P < 0.01). Fever, occurring first, and anorexia may be useful in early BRD diagnosis. However, in recently-arrived cattle, effects of acclimation should be considered when monitoring behavior for sickness detection.