THE SEROPREVALENCE OF MAEDI-VISNA IN ONTARIO SHEEP FLOCKS AND ITS RELATIONSHIP TO FLOCK DEMOGRAPHICS AND MANAGEMENT-PRACTICES

The objectives of this study were to describe the serological prevalen ce of maedi-visna in a sample of Ontario sheep flocks, and to identify management and demographic variables that were associated with seropr evalence for maedi-visna. A sample of 103 sheep flocks in Ontario was randomly selected from those flocks participating in the Red Meat Plan . The owners of these flocks were surveyed regarding management proced ures on their farms, and blood samples were taken from a random sample of ewes in each flock. At least one ewe tested serologically positive , based on the agar gel immunodiffusion test, in 69.9% of the farms. P ositive serological reactions occurred in 20.9% of the 3880 sheep test ed. Flock demographics and farm management variables were considered i n a multiple regression model, and several factors were positively ass ociated with higher maedi-visna seroprevalence rates. These included t he average age of the flock, the number of years the owner had been sh eep farming, the practice of using foster ewes, the practice of allowi ng lambs to have contact with other ewes that are lambing, and the ave rage pasture acreage per ewe.