Quantitation of Bovine Viral Diarrhea Virus in Embryo Transfer Flush Fluids Collected from a Persistently Infected Heifer

Abstract

Due to the epidemiological significance of persistently infected animals, it is important that possible methods of transmission be investigated. Currently, the recommended prevention and control measures for BVDV are centered around the identification and removal of persistently infected animals and the judicious use of BVDV vaccines. 4,6 Unfortunately, the identification of persistently infected animals has not been emphasized until recently and remains impractical. The purpose of this report is to emphasize the epidemiological significance of animals persistently infected with BVDV, especially in relation to embryo transfer procedures. A 5-month-old Holstein heifer, persistently infected with BVDV, was identified in a dairy herd with a history of BVDV infection by virus isolation from nasal and vaginal swabs and serum. The heifer had no detectable levels of BVDV serum antibodies (in indirect fluorescence assay [IFA]) and was kept in isolation for observation and testing. Estrus first was detected at 14 months of age. Following the third heat cycle the heifer was superovulated with follicle-stimulating hormone (days 11-14) and inseminated with BVDV-negative semen (confirmed negative by virus isolation) during the subsequent estrous. Embryo collection was attempted on day 7 (estrus day 0) by standard whole body uterine flush using 2 liters of Dulbecco’s phosphate-buffered saline containing 3% BVDV-negative fetal bovine serum (confirmed negative by virus isolation). Virus was not isolated from the flush medium prior to the uterine flush. Only 3 unfertile eggs were identified by microscopic examination in the uterine flush fluid (2 liters). The titers of BVDV were quantitated in various samples collected from the persistently infected heifer by virus isolation from 10-fold dilutions of the samples. One milliliter of each dilution was inoculated in replicates of 3 onto BVDVnegative secondary bovine turbinate cells passaged 5-10 times in Dulbecco’s minimum essential medium containing 10% horse serum. The inoculum was removed after 1 hour and