Bovine pestivirus infection: a cause of ovulatory disturbance in dairy cows

Twelve (Experiment I) and four (Experiment II) multiparous dairy cows seronegative to pestivirus were selected and randomly assigned to either a control group which did not become infected or a treatment group in which all cows became infected following intranasal inoculation 9 days before AI. The experimental induction of infection was carried out with 2 ml of non-cytopathic pestivirus (BVD virus) suspension containing 5 log10 TCID50/ml (Experiment I) and 4.5 log10 TCID50/ml (Experiment II). In both experiments, the cows were superovulated on day 10±2 of the cycle using the standard procedures. The cows in Experiment I were artificially inseminated at 12 and 24 h after the onset of estrus and a non-surgical ova/embryo collection was performed 7 days after AI. In Experiment II, the cows were slaughtered on day 8 after superovulation-induced estrus and the ovaries submitted for gross and histopahological examination including immunohistochemistry. Mean (±SE) number of ovulatory sized follicles on day of AI and corpora lutea palpated on day 7 after AI were significantly (p<0.05) higher in control un-infected cows compared to that of the pestivirus infected cows (17.1 ± 2.6 vs. 9.2 ± 1.1 and 12.2 ± 2.7 vs. 2.8 ± 0.9), respectively. On histopathological examinations, the mean (±SE) number of unovulated lutenised follicles (≥ 9mm in diameter) present on the ovaries of the control cows on day 8 after estrus was 6.8±4.9 compared to 12.5±5.4 for the infected cows. Further, many corpora lutea in the ovaries of infected cows had a hypoplastic or atrophic wall. In conclusion, the present study demonstrated that pestivirus infection during the period of final growth of preovulatory follicles results in a disturbance in ovulation and development of corpus luteum leading to a poor superovulatory response in multiparous dairy cows.