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

Footrot is one of the top five globally important diseases of sheep and causes lameness, leading to poor welfare and productivity. Transmission of <i>Dichelobacter nodosus</i>, the causative agent, occurs via surfaces such as pasture or bedding and persistence occurs from diseased sheep shedding bacteria into the environment; <i>D. nodosus</i> cannot replicate off host. High resolution proximity sensors were deployed on a flock of Poll Dorset sheep for 10-17 days at several points of the production cycle (teasing, tupping, pregnancy, and lactation (<6-week-old lambs)) between July 2018 and May 2021. Association indices between pairs of sheep were calculated, and outbreaks of footrot were simulated using a network-based susceptible-exposed-infected-recovered model. Two management approaches were modelled (1) where sheep were treated either not promptly, or effectively, resulting in long recovery times (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. Under 'active management' conditions (scenario 2), outbreak sizes were smaller at all points of the production cycle. This adds to existing evidence that prompt, effective treatment of sheep at all stages of the production cycle is key to reducing the prevalence of footrot in the flock, including at breeding when sheep are more likely to be in close contact.