Introduction.

The recent isolation of M. a. paratuberculosis from non-ruminant wildlife species opens up the possibility of wildlife to domestic ruminant transmission via the faecal oral route. Here we determine the level of contact between cattle and rabbit faeces in the grazing environment (Exp 1) and between cattle and rodent faeces via farm-stored concentrate feed (Exp 2).

Methods.

The rates of deposition of rodent faeces in farm stored feed and rabbit faeces on grazing pastures on four farms with a history of paratuberculosis in cattle and wildlife were estimated by random stratified quadrat sampling. Exp 1: Remote behaviour-monitoring systems in conjunction with stratified surveys of sward height were used to quantify the grazing behaviour of 57 cattle in relation to rabbit faeces-contaminated pasture. Prior to grazing each field, 4 pasture treatments were created by contaminating 40 plots (0.5x0.5m2) with 0, 10, 50 or 250 rabbit faecal-pellets. Exp 2: Ten cattle were presented individually with 3 repeats of 5 feed treatments: 3 levels of contamination of concentrate feed (none, 20 and 80 faecal-pellets/400g feed) x two rodent species (rat and mouse).

Results.

The mean number of faecal-pellets deposited by adult rabbits on pasture was 7357?2571 faeces/ha/day. Grazing cattle did not avoid rabbit faeces and 54/57 cattle were recorded grazing seven 250-faecal-pellet plots. The mean number of faecal-pellets deposited by rodents in stored feed was 79.9 (95% CI: 37.5-165.9) faeces/m2/month. Cattle ingested 42% and 82% of rat and mouse faecal-pellets during Exp 2, respectively.

Discussion.

Given that rabbit faeces contains up to 4x10⁶ cfu M. a. paratuberculosis/g and the experimental doses needed to produce disease in domestic ruminants range from 10³ to 10⁹ organisms, the ingestion of a few wildlife faecal-pellets may constitute an infective dose for cattle. Current evidence suggests that rabbits pose the greatest wildlife risk of paratuberculosis to cattle.