Abstract :
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.
