Social networks respond to a disease challenge in calves

Abstract

Changes in network position and behavioral interactions have been linked with infectious disease in social animals. Here, we investigate the effects of an experimental disease challenge on social network centrality of group-housed Holstein bull dairy calves. Within group-housed pens (6/group) calves were randomly assigned to either a previously developed challenge model, involving inoculation with Mannheimia haemolytia (n = 12 calves; 3 calves/group) or a control involving only saline (n = 12 calves; 3 calves/group). Continuous behavioral data were recorded from video on pre-treatment baseline day and for 24 h following inoculation to describe social lying frequency and duration and all active social contact between calves. Mixed-model analysis revealed that changes in network position were related to the challenge. Compared to controls, challenged calves had reduced centrality and connectedness, baseline to challenge day. On challenge day, challenged calves were less central in the directed social contact networks (lower degree, strength and eigenvector centrality), and initiated contact (higher out-degree) with more penmates, compared to healthy calves. This finding suggests that giving rather than receiving affiliative social contact may be more beneficial for challenged calves. This is the first study demonstrating that changes in social network position coincide with an experimental challenge of a respiratory pathogen in calves.

Figure 1

Diagnostic box plots represent the relationship between social network measures and an experimental challenge model (inoculation with M. haemolytica) or a sham procedure (inoculation with sterile saline) of bull calves (35.9 ± 8.8 d of age) housed in groups (6 calves/pen). Each plot shows the mean and distribution centrality network metrics (a) strength centrality, (b) degree centrality, (c) eigenvector centrality plotted for “challenged” (MH) and “healthy” (CON) individuals in each Pen (X-axis). Figure was created using R.

Figure 2

Network representation of the ‘All-Social Contacts Frequency’ networks of group-housed (n = 6/pen) bull calves (35.9 ± 8.8 d of age) exposed to an experimental challenge model (inoculation with M. haemolytica) or a sham procedure (inoculation with sterile saline): (a) baseline day: Pen#1–Pen#4, versus (b) challenge day: Pen#1–Pen#4. Individual calves (nodes) are represented by the circles; size is based on strength centrality; lines represent the weighted interactions among penmates. Baseline centrality scores were significantly different from centrality scores on challenge day and these differences were related to health. Figure was created using R.