Sequential studies of bovine leukemia virus antibody development in dairy cattle over a four-year period.

Serological examinations using the agar gel immunodiffusion and immunofluorescence tests were undertaken to study: a) the development of bovine leukemia virus infections in a given herd under field conditions monitored by antibody development, b) the reproducibility of the results of serological examination during 22 sequential tests, c) the antibody titre variations amongst individual animals. A total of 286 Friesian cattle representing 2,352 serum samples was tested at regular intervals over a period from 1974/75 to 1978. The percentage of animals with bovine leukemia virus antibodies continuously increased during the observation period from an initial 4.8% (1974/75), 9.7% (1976), 34.2% (1977) to 52.6% (1978). On the basis of 22 sequential tests representing 1,672 serum samples obtained from 76 animals no false positive reactions were seen in the immunodiffusion test. Thirty-six (14.2%) out of 254 animals, however, showed variations of the antibody titre leading to a shift from positive to negative or negative to positive results, respectively. AnothFr three cattle (1.2%) shifted from a positive to negative immunodiffusion result and maintained their negative reactivity for at least two following tests. But they still had specific antibodies if tested by the immunofluorescence test. A detailed analysis of the group of variable reactors supports the view that a more sensitive and quantitative test system may be helpful to complement the presently used immunodiffusion test for the eradication of enzootic bovine leukosis.