Role of Rabbits and the Environment in the Epidemiology of Paratuberculosis of Farmed Ruminants. (FF)

An indoor controlled grazing experiment was carried out to quantify the rate of ingestion of rabbit faeces during grazing by cattle and sheep. Recently weaned calves and sheep were offered swards of three different sward heights (3, 6 and 12 cms) contaminated with three different levels of rabbit faecal pellets. Overall, calves ingested 1.27% of the faecal pellets presented with individuals ingesting between 16 and 56 pellets in total. There was no significant effect of the level of contamination on the proportion of pellets ingested resulting in more faeces being ingested as the level of contamination increased.
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Lambs appeared to be more selective than calves, ingesting only 0.476% of the pellets presented to them with individuals ingesting between 1 and 6 pellets in total. In contrast to the calves the proportion of faecal pellets ingested decreased as the level of contamination increased.
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Combining the experimental data with field information it is postulated that cattle have the potential to ingest between 140-1329 infected rabbit faecal pellets per hectare grazed and sheep the potential to ingest 53-498 faecal pellets per hectare grazed. Therefore the level of exposure of grazing herbivores to infected rabbit faecal pellets is high.
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Field studies to determine the dynamics of paratuberculosis in wild rabbit populations continued. Mycobacterium avium subspecies paratuberculosis was recovered from approximately 40% of rabbits examined. Initial results from the cultures of organs suggest vertical and pseudovertical routes of transmission are highly possible.
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Work was initiated in developing a spatially explicit simulation model for paratuberculosis infection in rabbits. This incorporates information on rabbit social structure, rabbit mating, rabbit mortality and rabbit dispersal into which will be added the information on the routes of transmission.