Maedi-visna control in sheep III: Results and evaluation of a voluntary control program in the Netherlands over a period of four years.

Summary The results of the first four years of the Dutch national voluntary maedi‐visna control program, which was launched on January 1, 1982, are presented. At the end of the observation period, 1711 breeding flocks representing 70% of the registered breeding flocks participated. The program is based on accreditation of flocks that have passed two successive serological tests with an interval of six months between and post‐accreditation tests every 12 months. The flocks have to conform to a set of specific regulations. Sheep sold from such flocks receive a certificate stating that their origin was accredited. A total of 1212 flocks gained accredition. Of these flocks, 29.5% were free from infection from the beginning, 35.6% were created by total replacement of the original stock, 19.6% employed repeated testing and culling of positives, and 15.3% were created by artificial rearing of colostrum‐deprived lambs. A total of 22 flocks lost accreditation due to detection of 36 seropositives. These positives a...