The present invention relates to mutant Bovine Herpesvirus 4 genomes, mutant Bovine Herpesvirus 4 viruses, to mutant Bovine Herpesvirus 4 genomes and viruses carrying a heterologous DNA sequence, cells transfected with mutant Bovine Herpesvirus 4 genomes, cells infected with mutant Bovine Herpesvirus 4 viruses, vaccines and carrier vaccines comprising such mutant Bovine Herpesvirus 4 viruses, methods for the preparation of such mutant Bovine Herpesvirus 4 genomes and such mutant Bovine Herpesvirus 4 viruses and to diagnostic test kits.