Implication of complex vertebral malformation and bovine leukocyte adhesion deficiency DNA-based testing on disease frequency in the Holstein population.

Two inherited lethal disorders, bovine leukocyte adhesion deficiency (BLAD) and complex vertebral malformation (CVM), play a major role in breeding of Holstein cattle. Both inherited diseases are based on single nucleotide polymorphisms that have been known for 12 and 7 yr, respectively. A total of 25,753 cattle were genotyped for BLAD (18,200 tests) and CVM (14,493 tests) in our laboratory since the beginning of the genotyping programs for these diseases. Based on founder effects, the CVM mutation is thought to be linked to milk production. The BLAD was genotyped using RFLP until 2001; then a fluorescence resonance energy transfer assay on a LightCycler was used, as for CVM genotyping. By using single nucleotide polymorphism-aided breeding, the allelic frequency of the BLAD and CVM mutations in the active sire population was reduced from 9.4% in 1997 to 0.3% in 2007 (BLAD) and from 8.3% in 2002 to 2.3% in 2007 (CVM), with calculated half-life of the mutant allele of 2.1 yr for BLAD and 3.6 yr for CVM. An observed increase of BLAD frequency in 1999 could be attributed to the massive use of a BLAD-positive sire tested falsely negative in another laboratory. These data show that marker-assisted selection is capable of substantially reducing the frequency of a mutation within a period of not more than 5 yr. The different selection strategies against the lethal recessive allele in CVM and BLAD are reflected in the different reduction rates of the specific allele frequencies.