Simple control strategy to reduce the level of Maedi-Visna infection in sheep flocks with high prevalence values (>90%)

6 páginas, 1 tabla, 2 figuras.The presence of Maedi-Visna disease in sheep flocks have a significant economic impact, thus the aim of this study was to carry out a serological evaluation of a simple epidemiological control method for ovine Maedi-Visna infection in an intensive dairy flock with high initial seroprevalence. The study population was made up of an initial flock of 197 Spanish Assaf sheep kept in permanent housing using an intensive milking system, and the subsequent five generations of offspring. The control strategy used in this study was mainly based on separating the offspring from the dams after natural intake of colostrum using artificial rearing with milk replacer. Then, replacement groups were formed by these lambs, which were housed in the same shed as the rest of the flock, but in addition, other control measure applied in this study was the isolation of the replacement group from the adults by a barrier (1.20. m high metal sheet) that prevented physical contact between them in the housing, although airspace was shared. Then, replacement groups did not join the adult flock until the onset of first lactation (around 12 months-old). Control measures were first established in 2006 with the second generation offspring, leaving the first replacement group as the control group. Serum samples from all sheep in the flock were screened every six months for antibodies against Maedi-Visna virus using an immunoenzymatic assay. After the application of this control programme, seroprevalence had declined significantly from 93.1% to 54.2% in four years. Results from this study indicate that these control measures may offer a simple alternative for reducing high levels of prevalence in these dairy sheep flocks. Thus, this control strategy is proposed as the first control measures to be taken in flocks with a high prevalence of infection where no other measures could be reasonably applied, followed and expanded by other effective methods when the seroprevalence status of the flock permitting. © 2012 Elsevier B.V.This work was supported by grants from the Spanish Ministry of Education (AGL2007-66874-CO4-04/GAN) and from the Junta of Castilla y León (LE36A12-1). L. Polledo holds a grant from the Ministry of Education (AP2007- 02007). We thank Luis Fernando de la Fuente Crespo for his collaboration in the statistical study, Gloria Belver for technical assistance, and Donal Savage for revising the lenguage of the manuscript.Peer Reviewe