Field evidence of roof rat (Rattus rattus) faecal contamination of barley grain stored in silos in the Czech Republic

This study represents the first European report of a risk assessment for the contamination of grain by roof rats’ (Rattus rattus L.) faeces in silo structures that have traditionally been considered to be rodent-contaminant proof. In this work, we estimated the rate and magnitude of grain and grain transport silo technology contamination by faeces of R. rattus and identified the routes of entry of rodent faeces into grain stored in silos. We also compared the sizes of rat faeces and stored barley grains to determine whether they could easily be separated using sieves. We found that roof rats were able to heavily contaminate grain surfaces and conveyor belts with faecal deposits during a 3-week observation period. The average contamination rate was 6.90 ± 0.92 faeces/m2 (range 0–26 faeces/m2) for grain surfaces and 34.80 ± 8.03 faeces/m2 (range 8–87 faeces/m2) for conveyor belts. The size measurements (length, width and surface area) of rat faeces and barley grains showed their high similarity; these results therefore indicate that the physical separation of the two materials using sieves will be problematic.