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 ̂ days before AI. The experimental induction of infection was carried out with ˻ ml of non-cytopathic pestivirus (BVD virus) suspension containing ̋ log ˺˹ TCID ̋˹ /ml (Experiment I) and ̊̄̋ log ˺˹ TCID ̋˹ /ml (Experiment
... ̋˹ /ml (Experiment II). In both experiments, the cows were superovulated on day ˺˹˻ of the cycle using the standard procedures. The cows in Experiment I were artificially inseminated at ˺˻ and ˻̊ h after the onset of estrus and a non-surgical ova/embryo collection was performed ̀ days after AI. In Experiment II, the cows were slaughtered on dayáfter dayáfter 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 ̀ after AI were significantly (p<˹̄˹̋) higher in control un-infected cows compared to that of the pestivirus infected cows (˺̀̄˺˻̄̌ vs ̂̄˻˺̄˺ and ˺˻̄˻˻̄̀ vs ˻̄́˹̄̂), respectively. On histopathological examinations, the mean (±SE) number of unovulated lutenised follicles (≥ ̂mm in diameter) present on the ovaries of the control cows on dayáfter dayáfter estrus was ̌̄́̊̄̂ compared to ˺˻̄̋̋̄̊ 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.