[BLIRD - a new genetic disease in Holstein cattle in Switzerland].

Introduction: Recently, a new hereditary disease, bovine lymphocyte intestinal retention defect (BLIRD), was discovered in Holstein cattle in France and is caused by a variant in the Integrin subunit beta 7 (ITGB7) gene. The altered cell adhesion molecule resulting from this point mutation is responsible for an impaired tissue of CD4 T lymphocytes from the blood to intestinal tissue. The aim of this study was to assess the allelic frequency of this deleterious variant in the local Holstein population and to clinically examine ten BLIRD-affected Holstein cattle from Switzerland in order to characterise the phenotype of this new hereditary disease, which is still unknown to the veterinary community. BLIRD was associated with severely impaired animal health in the rearing phase and significantly reduced animal welfare due to weakened immune defences, below-average development and recurrent diarrhoea. Further examinations revealed increased leucocyte values and a slightly increased average age at first calving. Affected homozygous animals are labelled internationally as BLIRD-carrier homozygous (LRS), BLIRD-carrier heterozygous (LRC) and BLIRD-free (LRF). An obvious inbreeding practice was clearly demonstrated by the pedigree analysis of the ten animals, which all trace back to the potential founder bull. Herein, BLIRD has been detected and described in Switzerland for the first time. The ITGB7 variant allele has a frequency of 2,1 % in the current Swiss Holstein population, which is below the level of the cholesterol deficiency (CD)-associated apolipoprotein B (APOB) variant allele with a frequency of 3,9 %. Although relatively rare, attention should be paid to the BLIRD genotype when mating in order to exclude further affected animals. In cattle with clinically suspected BLIRD, the diagnosis should be confirmed by genetic testing.