Abstract: A recombinant virus is provided which is obtained from a BHV virus originally having the gI gene whose DNA sequence is delimited by nucleotides 172 and 1311 of SEQ ID NO:1 herein and which has been mutated by total or partial deletion and/or insertion in this region. By the mutation in this region, there is no longer any expression of the glycoprotein which has been mutated or rendered inactive, and thus animals vaccinated with these mutants do not develop antibodies against the glycoprotein and can be serologically distinguished from animals infected by field BHV-1 strains and other vaccinal strains currently used. A method of using the present recombinant virus is also provided which allows one to distinguish infected animals from vaccinated animals in a manner that has not previously been possible using presently available commercial vaccines.