Seasonal variations in physical contact amongst domestic sheep and the implications for disease transmission

Contact networks can provide useful insights into animal behaviour and have the potential to quantify the spread of disease. Successful control of livestock diseases requires an understanding of how they spread amongst animals and between premises. Whilst movement records can provide valuable data on potential between-farm spread, the within-group dynamics of livestock are not well quantified; without this knowledge it is difficult to fully exploit knowledge about one-to-one transmission (such as insights gained from small scale experiments). Here the physical contact structure of domestic sheep (Ovis Aries) flocks is determined for different stages in the breeding cycle. Three observational studies were carried out on conventionally managed flocks, consisting of approximately thirty Dorset/cross sheep grazing a large paddock: a flock with young (newborn) lambs and their mothers; the flock when the lambs were older (nearly weaned); and a flock of ewes outside of the lambing season. Networks were constructed and key centrality measures calculated for all direct physical and proximal contacts. Proximity networks with conventional sheep flocks appear to be dense, but physical contacts have a more complex structure with strong variations determined by stages in the breeding cycle. There was a significant difference in the level of physical contact within those flocks with lambs and those without, and also as a result of the age of lambs. A clear reduction in between-ewe contact was observed amongst individuals with young, but there was an overall increase in connectivity in such flocks as a result of contacts involving lambs. Results are considered applicable to different sized flocks, given the known social behaviour of sheep and the experimental protocol used.