The effect of bovine pestivirus infection on the superovulatory response of Friesian heifers.

The pathogenesis of reproductive loss associated with bovine pestivirus infection during the preovulatory period was investigated using superovulated heifers. Twenty-five Friesian heifers were selected and randomly assigned to either a control group (n = 12) which did not become infected or to a treatment group (n = 13) which became infected following intranasal instillation of 2 ml of serum inoculum containing 5.5 log(10) TCID(50)/ml non-cytopathic virus, 9 d prior to artificial insemination (AI). Transrectal ultrasonography was used to monitor follicular development and ovulation during the superovulatory period. Animals were superovulated using a standard protocol of twice-daily injections of FSH-P and then were inseminated twice commencing 12 h after the onset of estrus. The intensity of expression of estrus was higher in the control heifers than in the pestivirus-infected heifers. Of 13 pestivirus-infected heifers, only 3 heifers displayed standing estrus compared with that in the control group, in which 10 of 12 heifers exhibited standing estrus. The mean number of ova/embryos recovered from the control group heifers was 5.75 +/-2.31, of which 4.00 +/- 0.72 were evaluated as transferable quality embryos. In comparison, heifers in the pestivirus-infected group yielded only a mean of 0.60 +/-0.34 ova/embryos, of which 0.23 +/- 0.22 were transferable quality embryos. Based on ultrasonographic examination, 24 h after the first AI 82% of the presumptive ovulatory follicles had ovulated in the control group compared with an ovulation rate of only 17% in the treated group. The results of this experiment demonstrated that bovine pestivirus infection during the preovulatory period could adversely affect ovulation, thus leading to a significant reduction in the number of palpable corpora lutea and in the number and quality of embryos recovered.