Equine herpesviruses 1 and 4 (EHV-1 and EHV-4) cause equine respiratory disease worldwide. However, only EHV-1 is a cause of abortion and neurological disease, despite the two viruses having all 76 genes in common. In addition EHV-1 has a broader host range in cell culture than EHV-4, as exemplified by the rabbit kidney (RK) cell line that is permissive for EHV-1, but not for EHV-4. Here we describe that when EHV-4 produced in equine cells was inoculated onto RK cells expressing glycoprotein D of EHV-1 (RKgD1), infection developed as clusters of rounded cells, and this infectivity could be passaged in RKgD1 cells. The progeny virus could also infect single RK cells, consistent with EHV-4 acquiring EHV1∈gD from the complementing cell line. No such infection was observed for EHV-4 in RK cells expressing EHV-1 glycoprotein C. The results are consistent with gD homologues being major determinants of host cell tropism and raise the possibility that gD may be a factor in the differential pathogenicity of EHV-1 and EHV-4.