The results are presented of testing untreated producer–retailer herd milk samples for the presence of Brucella abortus during the period 1965–1972 in the North Lancashire region.
There was a steady decline in the incidence of infected herds from 22 % in 1965 to 12% in 1971. A sharp fall to 5% in 1972 suggests that the introduction of the Brucellosis Incentives Scheme and the eradication programme has helped to reduce the practice of selling brucella-infected cattle in the open market which was prevalent in the period 1965 to 1970.
This practice of selling brucella-infected cattle may also be a prime factor in the changing pattern of distribution of the biotypes of B. abortus which was observed during the period 1965 to 1970.
A comparison of the two areas in the region show that the incidence of herd infection was always greater in the area containing flying herds than in the area in which self-contained herds predominated.