Proceedings of the 10th International Colloquium on Paratuberculosis

#88
Influence <strong>of</strong> between-calves contacts on Mycobacterium avium paratuberculosis (Map)
transmission in a dairy herd
Clara Marce, Pauline Ezanno, Henri Seegers, Dirk Udo Pfeiffer, Christine Fourichon
INRA, Veterinary School <strong>of</strong> Nantes, France; Royal Veterinary College <strong>of</strong> London, United Kingdom
Mycobacterium avium paratuberculosis (Map) can be transmitted from adults to calves. In <strong>the</strong> dairy industry,
calves are rapidly separated from <strong>the</strong>ir dam and are not raised in contact with adults. Calf-to-calf transmission
has recently been reported. However, <strong>the</strong> role played by this route <strong>of</strong> transmission has not been evaluated yet,
despite <strong>the</strong>re being extensive opportunity <strong>of</strong> contact as calves are usually raised toge<strong>the</strong>r. Our objective was to
assess <strong>the</strong> effect <strong>of</strong> contact structure between calves on Map transmission and to specifically assess <strong>the</strong> effect
<strong>of</strong> calf isolation during <strong>the</strong> first weeks <strong>of</strong> age, while taking account <strong>of</strong> o<strong>the</strong>r transmission pathways. We used a
stochastic compartmental model with discrete time steps to represent Map spread in a closed dairy herd after
<strong>the</strong> introduction <strong>of</strong> an infected heifer. A dairy herd management system was modelled with calves being housed
in individual pens before being moved to collective pens. Grazing was allowed during pasture season and
after 6 months <strong>of</strong> age. Vertical and horizontal transmission from adults (classified in 3 infectious statuses) and
from transiently infected calves could occur. Indirect transmission via <strong>the</strong> environment was explicitly modelled.
Influence <strong>of</strong> herd size and <strong>of</strong> <strong>the</strong> time spent by calves in individual pen on contact structure was studied. Three
herd sizes were considered for which <strong>the</strong> number <strong>of</strong> collective pens before and after weaning differed. The
time spent in individual pen was assumed to vary from 0 to 8 weeks in compliance with EU regulation. Infection
mainly occurred via vertical transmission or adult-to-calf horizontal transmission through <strong>the</strong> ingestion <strong>of</strong> faeces
present in <strong>the</strong> environment. Effects <strong>of</strong> <strong>the</strong> time spent in individual pen before being moved to collective pen on
<strong>the</strong> persistence <strong>of</strong> Map and on within herd prevalence suggest that it is more important to consider hygiene
management than contacts in calf housing facilities.
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