Evaluation of two management procedures for the control of maedi-visna.

Two control programs were evaluated for their efficiency in eradicating the maedi-visna (M-V) virus from a single sheep flock. In both programs, the agar gel immunodiffusion test was used for the detection of M-V infected animals at regular intervals. In program 1, the test and remove program, ewes that were serologically positive for M-V were immediately removed along with their offspring. The prevalence of infected sheep decreased gradually and a seronegative flock was obtained after 30 months of monitoring. Program 2 entailed the removal of replacement ewe lambs at birth prior to the ingestion of colostrum. Maedi-visna antibodies have not been detected in this flock. These results show that under conditions similar to the industry norms, M-V can be expelled. Although the approach of program 1 is more practical for sheep producers, program 2 is more effective because of the earlier development of a M-V seronegative flock. Because of the nature of the humoral response, a longer time period than four years is required to ensure that M-V has been completely eradicated from each flock.