RESUMEN
The aim of the study was to investigate the effect of Bovine Herpesvirus 4 (BoHV-4) and Histophilus (H.) somni on fertility rate of cows in a Hungarian Holstein-Friesian dairy herd with purulent vaginal discharge (PVD). Non-pregnant cows (n = 188) with mature corpus luteum were treated with cloprostenol and 3 days later if they did not show oestrus, were examined by rectal palpation. Animals showing PVD (n = 60/31.9%/) and 14 controls with normal vaginal discharge (Score 0) were randomly selected and further examined by ultrasonography and blood samples were collected for detecting BoHV-4 DNA and transcervical guarded swabs were collected from the uterus for bacteriological examination. Although the majority of the examined animals were infected with BoHV-4 and H. somni including the control animals as well, in group of animals with PVD score 3, fewer animals became pregnant and the duration between the first treatment to pregnancy was significantly extended. Based on these clinical and comparative data, our results confirm that these two microorganisms together may impair important reproductive parameters which may cause large economic losses to dairy farms.