An improved DNA test for bovine leucocyte adhesion deficiency.

A modified DNA test, based on the polymerase chain reaction, was developed for the monogenic recessive disease bovine leucocyte adhesion deficiency (BLAD). The test was improved by the selection of new primers which facilitated the interpretation of the results. An easily scorable banding pattern makes the test useful in cattle breeding schemes and for clinical diagnosis. A total of 2381 samples was analysed over a period of three years. The carrier rate among young bulls at artificial insemination (AI) stations decreased from 11.6 per cent in 1993 to 9.9 per cent in the first five months of 1995. Continuous screening of young bulls before entering AI is still recommended unless both parents are proven to be genetically free of BLAD. The carrier rate among clinically suspect animals was not increased, and carriers are therefore not expected to be immunodeficient. Despite all efforts to eradicate the disease, calves with BLAD were still observed in 1995.