Background: Epidemiological studies have used farmer estimates of the prevalence of lameness in their flocks. This assumes that farmers can identify lame sheep. Eight movie clips of sheep with locomotion from sound to moderately lame were used to investigate the ability of farmers and sheep specialists to recognise lame sheep. Each participant was asked to complete a form and indicate, for each movie clip, whether they thought the sheep was lame and whether they would catch it if it was the only lame sheep or if 2 - 5, 6 - 10 or > 10 sheep were equally lame. The farmers' responses were compared with their estimates of flock lameness prevalence and the interval between observing a lame sheep and catching it.
Results: 178 farmers and 54 sheep specialists participated. Participants could identify even mildly lame sheep but made a separate decision on whether to catch them. This decision was dependent on the severity of lameness and the number of sheep lame in a group. Those who said they would catch the first lame sheep in a group were significantly more likely to catch mildly lame sheep (farmer-reported median prevalence of lameness 5% (IQR: 2%-6%)). In contrast, farmers who waited for several sheep to be lame indicated that they would only catch more severely lame sheep (farmer reported median flock lameness 11% (IQR: 9%-15%)). Approximately 15% of farmers did not catch individual lame sheep (farmer reported median flock lameness 15% (IQR: 10%-15%)). The flock prevalence of lameness increased as time to treatment increased and time to treatment was positively correlated with only catching more severely lame sheep.
Conclusion: If movie-clips are similar to the flock situation, farmers and specialists can recognise even mildly lame sheep but vary in their management from prompt treatment of the first lame sheep in a group to no individual sheep treatments. The former practices would be appropriate to minimise transmission of footrot, a common, infectious cause of lameness and so reduce its incidence. The analysis also suggests that farmers estimate lameness prevalence relatively accurately because farmers who treated the first mildly lame sheep in a group also reported the lowest prevalence of lameness in their flock.