Vet. Res. 37 (2006) 767-778
DOI: 10.1051/vetres:2006034

Extensive rearing hinders Maedi-Visna Virus (MVV) infection in sheep

Iratxe Leginagoikoa^a, Ramón A. Juste^a, Jesse Barandika^a, Beatriz Amorena^b, Damián De Andrés^b, Luis Luján^c, Juan Badiola^c and Eduardo Berriatua<sup>a, d

a</sup>  Instituto Vasco de Investigación y Desarrollo Agrario-NEIKER, Derio, Bizkaia, Spain
^b  Instituto de Agrobiotecnología y Recursos Naturales, CSIC-UPNA, Pamplona, Spain
^c  Patología Animal, Universidad de Zaragoza, Zaragoza, Spain
^d  Enfermedades Parasitarias, Facultad de Veterinaria, Universidad de Murcia, 30100 Campus de Espinardo, Murcia, Spain

(Received 10 October 2005; accepted 3 May 2006; published online 15 September 2006)

Abstract - Maedi-Visna Virus (MVV) seroprevalence and its relationship with housing and mode of rearing of replacement ewe-lambs was investigated in 38 non-randomly selected sheep-flocks in Spain. They included extensive lamb-producing Manchega cross-bred flocks raised almost permanently at pasture, semi-intensive Latxa dairy flocks housed 2-8 months/year and intensively raised Assaf dairy flocks housed most time and at higher stocking density in less ventilated buildings than other flocks. Most flocks raised replacement lambs naturally with their dams until weaning and as a separate flock thereafter until lambing at one year of age. Seroprevalence (95% confidence intervals) was 77%, 25% and 5% (4-6) in intensive, semi-intensive and extensive flocks, respectively and the median (interquartile range) flock-seroprevalence was 82% (66-94) in intensive flocks, 31% (14-31) in semi-intensive flocks and 4% (0-7) in extensive flocks. Seroprevalence was lowest in one year-old sheep and increased to flock levels during the year after introduction into the adult flock in most intensive flocks and more gradually in other flocks. Adult flock seroprevalence was associated with housing time but this relationship was not evident within a particular rearing system, indicating that other unknown factors are critical in horizontal MVV-transmission. Low seroprevalence in extensive flocks further supports previous indications that lactogenic MVV-infection is relatively inefficient and horizontal transmission is necessary to ensure long-term maintenance of MVV and this could explain that MVV has not been reported from countries with mainly extensively reared sheep such as Australia and New Zealand. Moreover, it indicates that MVV-control in extensive and semi-intensive flocks can be simple and inexpensive.

Key words: Maedi-Visna Virus / sheep / seroprevalence / intensive and extensive rearing / Spain

Corresponding author: berriatu@um.es

© INRA, EDP Sciences 2006