Social Structure of Sheep Flocks at Points of the Production Cycle and Relationship to Disease Spread, Using a Simulated Epidemic of Footrot

Footrot is an infectious disease of sheep that causes lameness, reducing sheep welfare and costing farmers in terms of both costs of treatment and reduced productivity. While transmission of the causative agent, Dichelobacter nodosus, between sheep is likely indirect and occurs via infected pasture, little work has explored how heterogenous connections made by sheep within farm management groups are associated with disease transmission. The aim of this research was to simulate the spread of footrot on real-life social structures of sheep measured using high-resolution social contact data collected at several points of the production cycle: teasing, breeding, gestation, and lactation. We simulated two management scenarios reflecting different types of lameness management, (1) where sheep were treated either not promptly, or effectively, resulting in long recovery times and presence of chronically infected sheep (28-100 days) and (2) where sheep were treated and recovered within 15 days, assuming 'active management' of footrot by the farmer using 'best practice' of prompt recognition of lame sheep and parenteral and topical antibiotics. We show that the social structure of the flock varies both day to day and over the production cycle and that 'active management' of lameness results in smaller outbreak sizes at all stages of the production cycle, adding to the evidence base of the importance of 'active management' in reducing lameness levels in sheep flocks.