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

## TL;DR

This study shows that active management of footrot in sheep flocks reduces disease spread by simulating outbreaks under different treatment scenarios.

## Contribution

The novelty lies in using high-resolution social contact data to simulate footrot outbreaks and demonstrate the impact of active management on reducing outbreak sizes.

## Key findings

- Active management of lameness reduces outbreak sizes across all production cycle stages.
- Footrot transmission is influenced by the social structure of sheep flocks.
- Prompt treatment of lame sheep significantly lowers disease prevalence.

## Abstract

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.

Footrot is one of the top five globally important diseases of sheep and causes lameness, leading to poor welfare and productivity. Transmission of Dichelobacter nodosus, the causative agent, occurs via surfaces such as pasture or bedding and persistence occurs from diseased sheep shedding bacteria into the environment; D. nodosus 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.