In vitro fertilization and in vitro culture of bovine embryos in the presence of noncytopathic bovine viral diarrhea virus

Effect of Campylobacter fetus on in vitro fertilization and embryonic development of preimplantation bovine embryos

Campylobacter fetus is an important veterinary pathogen that causes campylobacteriosis. This disease causes decreased productivity of cattle by inducing reproductive losses. Although several virulence factors have been recognized in C. fetus, including a cytolethal distending toxin (CDT), the exact mechanism responsible for embryonic death remains unknown. The aim of this work was to evaluate the effect of C. fetus subsp. fetus (Cff) and C. fetus subsp. venerealis (Cfv), and their toxin activity on the in vitro fertilization of bovine ova and early embryonic development. Two different experiments were performed. In Experiment 1, a total of 1524 cumulus-oocyte complexes (COCs) were inseminated, distributed into three groups: two of them infected with the microorganism (Cff, Cfv) and a control group. Percentages COCs cleaved were similar among groups (p = 0.1243); however, the embryonic development rate (blastocyst at day 7) in the control group was greater (p < 0.001) than those obtained in Cff and Cfv groups. In experiment 2, a total of 746 COCs were inseminated, divided into three groups: two of them treated with the bacterial-free culture filtrates to test toxin activity (Cff-CDT, Cfv-CDT) and a control group. Both cleavage and embryonic development rates were greater (p < 0.001) in the control group than those obtained in Cff-CDT and Cfv-CDT groups. This study provides evidence that both subspecies of C. fetus do not interfere with fertilization but do affect in vitro embryonic development. It is the first report on the biological effect of the CDT on bovine embryonic development.

Mechanisms linking bovine viral diarrhea virus (BVDV) infection with infertility in cattle

Bovine viral diarrhea virus (BVDV) is an important infectious disease agent that causes significant reproductive and economic losses in the cattle industry worldwide. Although BVDV infection is known to cause poor fertility in cattle, a greater part of the underlying mechanisms particularly associated with early reproductive losses are not clearly understood. Previous studies reported viral compromise of reproductive function in infected bulls. In females, BVDV infection is thought to be capable of killing the oocyte, embryo or fetus directly, or to induce lesions that result in fetal abortion or malformation. BVDV infections may also induce immune dysfunction, and predispose cattle to other diseases that cause poor health and fertility. Other reports also suggested BVDV-induced disruption of the reproductive endocrine system, and a disruption of leukocyte and cytokine functions in the reproductive organs. More recent studies have provided evidence of viral-induced suppression of endometrial innate immunity that may predispose to uterine disease. Furthermore, there is new evidence that BVDV may potentially disrupt the maternal recognition of pregnancy or the immune protection of the conceptus. This review brings together the previous reports with the more recent findings, and attempts to explain some of the mechanisms linking this important virus to infertility in cattle.

Normal reproductive capacity of heifers that originated from in vitro fertilized embryos cultured with an antiviral compound

Bovine viral diarrhea virus (BVDV) can associate with in vitro fertilized (IVF) bovine embryos despite washing and trypsin treatment. An antiviral compound, DB606 (2-(4-[2-imidazolinyl]phenyl)-5-(4-methoxyphenyl)furan), inhibits the replication of BVDV in bovine uterine tubal epithelial cells, Madin Darby bovine kidney cells, and fetal fibroblast cells. As well, DB606 in in vitro culture medium does not affect embryonic development. Antiviral-treated-IVF embryos placed into recipients developed into clinically normal calves. The objective of this project was to determine if these resultant heifer calves were capable of reproducing. Seven heifers from each of the treatment groups (natural breeding, IVF embryo, and IVF embryo cultured in DB606) of the previous study were used. At 20-27 months of age, the heifers were exposed to a fertile bull in a single pasture during a 63 d breeding season. Five of the seven heifers originating from natural breeding were pregnant 35 d after removal of the bull and calved. All of the heifers resulting from transfer of untreated IVF embryos were pregnant at 35 d; however, one aborted the fetus at 5-7 months of gestation. All of the heifers derived from transfer of IVF embryos cultured in DB606 were pregnant and calved. Offspring from dams of all treatment groups were clinically normal at birth. Adjusted 205 d weaning weights were not significantly different among the offspring of the treated and untreated dams. These results indicate that culture of bovine-IVF embryos in DB606 does not impair future reproductive capacity of resulting heifers.

Development of a duplex quantitative polymerase chain reaction assay for detection of bovine herpesvirus 1 and bovine viral diarrhea virus in bovine follicular fluid

The objective of this study was to develop a duplex quantitative polymerase chain reaction (qPCR) assay for simultaneous detection of bovine herpesvirus 1 (BoHV-1) and bovine viral diarrhea virus (BVDV) type I and type II. Follicular fluid was collected from a BoHV-1 acutely infected heifer, a BVDV I persistently infected heifer, and from 10 ovaries recovered from an abattoir. Both the BoHV-1 and BVDV contaminated follicular fluid were diluted 1:5 to 1:10(7) using the pooled, abattoir-origin follicular fluid. Each dilution sample was analyzed using the duplex qPCR, virus isolation, reverse transcription-nested PCR (RT-nPCR), and BoHV-1 qPCR. The duplex qPCR was able to simultaneously detect BoHV-1 and BVDV I in the fluid diluted to 1:100 and 1:1000, respectively. These results corresponded with the reverse transcription-nested PCR and BoHV-1 qPCR. Therefore, the duplex qPCR might be used for quality assurance testing to identify these two viruses in cells, fluids and tissues collected from donor animals and used in reproductive technologies.

Risk assessment of transmission of bovine viral diarrhea virus (BVDV) in abattoir-derived in vitro produced embryos

Bovine virus diarrhea virus (BVDV) is a pathogen of the bovine reproductive system causing reduced conception rates, abortions and persistently infected calves. Most if not all strains of BVDV are transmissible by natural mating and AI. For international trade, it is recommended that in vitro fertilized embryos be washed according to the IETS Manual. However, BVDV may not be entirely washed out, resulting in possible transmission risks to recipients. Donor cows, donor bulls and biological agents are all possible sources of contamination. The process for producing in vitro produced (IVP) embryos is complex and non-standard, and some procedures can contribute to spread of BVDV to uninfected embryos. The structure of the zone pellucida (ZP) of IVP embryos permits adherence of BVDV to the ZP. To estimate the risk of producing infected recipients and persistently infected calves from abattoir-derived IVP embryos, a quantitative risk assessment model using Microsoft Excel and Palisade @Risk was developed. Assumptions simplified some of the complexities of the IVP process. Uncertainties due to incomplete or variable data were addressed by incorporating probability distributions in the model. Model variables included: disease prevalence; the number of donor cows slaughtered for ovaries; the number of oocytes collected, selected and cultured; the BVDV status of ovaries, semen, biological compounds and its behavior in the IVP embryo process. The model used the Monte Carlo method to simulate the IVP process. When co-culture cells derived from donor cows of unknown health status were used for in vitro culture (IVC), the probability of a recipient cow at risk of infection to BVDV per oocyte selected for IVP processing averaged 0.0006. However, when co-culture free from BVDV was used, the probability was 1.2 x 10(-5). Thus, for safe international trade in bovine IVP embryos (i.e. negligible risks of transmission of BVDV), co-culture cells, if used during IVC for producing IVP embryos, should be disease-free.

Detection of bovine viral diarrhea virus (BVDV) in single or small groups of preimplantation bovine embryos

The objectives of this study were to develop techniques to detect BVDV associated with single or small groups of bovine embryos contained in small aliquots of medium using either virus isolation (VI) or real time quantitative polymerase chain reaction (RT-QPCR) assays. In vivo-derived and in vitro-produced bovine embryos at 7 d post-fertilization were exposed to SD-1, a high affinity strain of BVDV, for 2 h and then processed according to the International Embryo Transfer Society (IETS) guidelines prior to testing. Groups of five or two in vivo-derived embryos, and single in vivo-derived embryos, were VI positive for BVDV 100, 50, and 33% of the time, and were RT-QPCR positive 100, 75, and 42% of the time, respectively. The virus was detected by the VI technique in all of the groups of five or two in vitro-produced embryos and in all of the single in vitro-produced embryos, and it was detected in 100, 80, and 50%, using RT-QPCR. Techniques for RT-QPCR were sufficiently sensitive to detect 10 copies of viral RNA in a sample and to detect BVDV associated with single embryos. Application of this new technology, RT-QPCR, will facilitate additional studies to further assess the risk of transmission of BVDV through embryo transfer.

Seroconversion of calves following intravenous injection with embryos exposed to bovine viral diarrhea virus (BVDV) in vitro

Two recent studies demonstrated that a high-affinity isolate of BVDV (SD-1), remained associated with a small percentage of in vivo-derived bovine embryos following artificial exposure to the virus and either washing or trypsin treatment. Further, the embryo-associated virus was infective in an in vitro environment. Therefore, the objective of this study was to determine if the quantity of a high-affinity isolate of BVDV associated with single-washed or trypsin-treated embryos could cause infection in vivo. Twenty zona-pellucida-intact morulae and blastocysts (MB) were collected on day 7 from superovulated cows. After collection, all MB were washed according to International Embryo Transfer Society (IETS) standards, and all but 4 MB (negative controls) were exposed for 2 h to 10(5)-10(6) cell culture infective doses (50% endpoint) per milliliter (CCID(50)/mL) of viral strain SD-1. Following exposure, according to IETS standards, one half of the MB were washed and one half were trypsin treated. All MB were then individually sonicated, and sonicate fluids were injected intravenously into calves on day 0. Blood was drawn to monitor for viremia and(or) seroconversion. Seroconversion of calves injected with sonicate fluids from washed and trypsin-treated embryos occurred 38% and 13% of the time, respectively. Therefore, the quantity of a high-affinity isolate of BVDV associated with single-washed or trypsin-treated embryos was infective in vivo.

Large scale assessment of the effect associated with bovine viral diarrhoea virus infection on fertility of dairy cows in 6149 dairy herds in Brittany (Western France)

This study aimed at quantifying on a large scale the risk of both three-week-return-to-service and late-return-to-service for dairy cows according to the BVDV-infection status of the herds. Three-week- and late-returns-to-service were defined as a repeat service occurring respectively from 19 to 25 days and after 25 days following a first or a second service. The level of BVDV-specific-antibodies in bulk tank milk were measured four times at four months intervals by a blocking ELISA test to define five BVDV-infection-herd-statuses: (i) presumed non-infected herds for a long time, (ii) presumed not-recently-infected herds, (iii) presumed past-infected-recently-recovered herds, (iv) presumed past-steadily-infected herds, (v) presumed recently-infected herds. A total of 150,854 AIs from 122,697 cows in 6149 herds was included in the analysis. The risk of return-to-service was assessed using logistic regression and survival analysis models. The BVDV-infection-herd-status was not significantly associated with the risk of 3-week-return-to-service, but significantly with that of late-return-to-service. Cows in herds presumed past-infected-recently-recovered, past-steadily-infected, or recently-infected had a significantly higher risk of late-return-to-service (relative risk of 1.03, 1.11, 1.12, respectively) compared with cows in herds presumed not-recently-infected. Risk of late-return-to-service was not significantly different in cows from herds presumed non-infected for a long time or not-recently-infected. In conclusion, BVDV-infection was found to mainly increase the risk of embryonic and foetal death.

In vitro maturation and fertilization of bovine oocytes and in vitro culture of presumptive zygotes in the presence of bovine pestivirus

A pathogen which has been shown to commonly contaminate in vitro bovine embryo production system is bovine pestivirus (bovine viral diarrhea virus). Three experiments were designed to evaluate the in vitro maturation (experiment I), fertilization (experiment II) and embryo development (experiment III) of immature oocytes, inseminated oocytes and presumptive zygotes in the presence of a bovine pestivirus (non-cytopathic, nCP type 1). The virus inoculum used was derived from a persistently infected cow. In experiment I, follicular oocytes (n=1257) recovered from slaughterhouse derived ovaries were randomly assigned to either a control group (n=578) which did not become exposed to bovine pestivirus and a treatment group (n=679) which was inoculated with bovine pestivirus (2.20-3.69 log(10) TCID(50)/50 microl) at the time of commencement of in vitro maturation. Overall, there was no significant difference between the control and pestivirus inoculated oocytes in either the cumulus cell expansion rate (79+/-7.5% versus 74+/-10.7%) or the nuclear maturation rate (89+/-4.8% versus 85+/-7.4%), respectively. In experiment II, in vitro matured oocytes (n=607) were inseminated either in the absence (control; n=301) or the presence of bovine pestivirus (4-4.6 log(10) TCID(50)/50 microl; n=306). A significant (P<0.01) reduction in the overall number of fertilized oocytes with two well formed male and female pronuclei was observed in the treatment group compared to the control group (58.5+/-5.8% versus 73.3+/-3.6%, respectively). In experiment III, after in vitro maturation and fertilization, presumptive zygotes were randomly assigned to either a control group (n=139) which was not exposed to bovine pestivirus or a treatment group which was inoculated with bovine pestivirus (2.97-4.47 log(10) TCID(50)/30 microl; n=139). The zygotes were then cultured under mineral oil in an atmosphere of 88% N(2), 7% O(2) and 5% CO(2) at 39 degrees C. The morphologic appearance of the embryos was assessed 48 h after the commencement of culture, and then every 48 h up to days 7-8 after insemination. The 22% (31/139) and 3.6% (5/139) of the presumptive zygotes developed to the morula or blastocyst stage in the control and the bovine pestivirus inoculated groups, respectively (P<0.001). This study demonstrates that bovine pestivirus has a significant detrimental effect on in vitro fertilization and early in vitro embryo development.

A strategy for rapid cooling of mouse embryos within a double straw to eliminate the risk of contamination during storage in liquid nitrogen

Double packaging, in which an inner straw containing the specimen is inserted into an outer, larger straw (here termed 'straw-in-straw') to prevent the inner straw from coming into direct contact with liquid nitrogen provides a simple strategy for reducing or eliminating the potential contamination risk associated with storage in liquid nitrogen. This approach has in the past been used in conjunction with cryopreservation by slow cooling, but has not previously been tested for use throughout an entire rapid cooling and warming procedure. This study determined whether keeping the straw containing the embryos inside a second protecting container throughout the cryopreservation and storage protocol would compromise embryo viability. We established that a cryoprotectant containing a high polymer concentration (35% dextran or Ficoll) together with 25% ethylene glycol (as the penetrating cryoprotectant) was highly effective for day 2 and day 3 mouse embryos in both single and double straws. The survival and development of all cryopreserved embryos, as assessed both in vitro and in vivo, was not statistically different to their untreated controls. This established that a protein/serum-free cryoprotectant solution supplemented with polymers could provide complete protection of mouse embryos. It also shows, for the first time, that embryos can be cooled by direct immersion in liquid nitrogen and warmed by direct immersion into a waterbath within a double straw arrangement to reduce the likelihood of contamination.

Replication and persistence of different strains of bovine viral diarrhea virus in an in vitro embryo production system

Recent studies have shown that exposed, in vitro-derived embryos remain contaminated with bovine viral diarrhea virus (BVDV) after washing. However, introduction of a Genotype II versus Genotype I strain of BVDV into an IVF system was reported to provide greater potential for transmission of disease. The primary objective of this study was to compare the potentials for different strains of noncytopathic BVDV to replicate in an IVF system, associate with IVF embryos and infect co-cultured cells via association with washed embryos. The secondary objective was to compare the effect of different strains of BVDV on embryonic development. Two Genotype I (SD-1 and NY-1) and 2 Genotype II (CD-87 and PA-131) strains of BVDV were evaluated. After IVM and IVF of oocytes, presumptive zygotes were washed and transferred into in vitro cultures containing uterine tubal cells (UTC) and medium that was free of BVDV-neutralizing activity. Immediately before addition of zygotes, the cultures were inoculated with 10(5) cell culture infective doses (50%, CCID50) of a strain of BVDV or maintained as a negative control. Cultures of zygotes were then incubated for 7 d. Embryonic development was observed on Days 3 and 7, and attempts were made to isolate BVDV from UTC and medium on Day 7. Also on Day 7, groups of intact, washed blastocysts were either transferred into virus-free secondary cultures containing UTC or sonicated with sonicate fluid assayed by both virus isolation and single-closed-tube reverse transcription nested polymerase chain reaction (RT-nPCR). After 3 d in secondary culture, hatched embryos were enumerated, and medium from the cultures, washed UTC and embryos were tested for BVDV by virus isolation. In addition, washed UTC and embryos were tested for BVDV using RT-nPCR. All strains of BVDV persisted and replicated in the embryo culture environment, but cleavage beyond the 4-cell stage, blastocyst development and hatching varied among cultures contaminated with different strains of virus. Further, the quantity of BVDV associated with washed embryos from both initial and secondary cultures varied among strains, but the variation was unrelated to difference in genotype (SD-1 and PA-131 greater than NY-1 and CD-87). Although all strains of BVDV replicated in UTC in the initial in vitro cultures and remained associated with washed blastocysts, susceptible UTC in the secondary in vitro cultures were seldom infected by any strain of virus.

The effects of bovine viral diarrhoea virus on cattle reproduction in relation to disease control

Bovine viral diarrhoea virus (BVDV) is a major reproductive pathogen in cattle. Infection of the bull can lead to a fall in semen quality and the isolation of infectious virus in the ejaculate, while infection in the cow leads to poor conception rates, abortions and congenital defects. BVDV also reduces the animal's resistance to other respiratory and enteric pathogens. The prevalence of BVDV is primarily due to the efficiency with which the virus crosses the placenta of susceptible females. Calves that survive infection during the first trimester of pregnancy are born with a persistent and lifelong infection. These persistently infected (PI) animals represent between 1.0% and 2.0% of the cattle population and continuously shed infectious virus. The availability of reliable diagnostic ELISA and PCR techniques, which can test milk or serum samples for virus or antibodies, has simplified BVDV surveillance and improved the prospects for control. Although PI animals are the principal vectors within and between herds, they can be readily identified and removed. By contrast, cows carrying a PI foetus are particularly problematic. These animals have been compared to 'Trojan Horses' because they are virus-negative and antibody-positive but they deliver PI calves. In general, acutely infected cattle are much less efficient vectors but infections at the onset of puberty have resulted in a localised and persistent infection within the testes. Under these circumstances, virus shedding into the semen may remain undetected. Transmission of BVDV can be controlled through vaccination or eradication. BVDV vaccine technology has been developing over the past 30 years, but currently available vaccines are still of the conventional inactivated or attenuated sort. In general, vaccination has not been applied with sufficient rigor to make a significant impact on the level of circulating virus, unlike the national and regional eradication programmes established in areas such as Scandinavia, Austria, the Netherlands and Scotland. Eradication confers the added advantage of improved herd health; however, it also creates a susceptible cattle population that needs to be protected by stringent biosecurity. In this article, we discuss how BVDV influences reproductive function, the potential for viral transmission during breeding and the measures that must be taken to avoid the spread of infection to susceptible cattle populations via semen, embryos, culture fluids and infected cows.

Quality controls for bovine viral diarrhea virus-free IVF embryos

Introduction of bovine viral diarrhea virus (BVDV) with cumulus-oocyte-complexes (COCs) from the abattoir is a concern in the production of bovine embryos in vitro. Further, International Embryo Transfer Society (IETS) guidelines for washing and trypsin treatment of in-vivo-derived bovine embryos ensure freedom from a variety of pathogens, but these procedures appear to be less effective when applied to IVF embryos. In this study, COCs were exposed to virus prior to IVM, IVF and IVC. Then, virus isolations from cumulus cells and washed or trypsin-treated nonfertile and degenerated ova were evaluated as quality controls for IVF embryo production. The effect of BVDV on rates of cleavage and development was also examined. All media were analyzed prior to the study for anti-BVDV antibody. Two approximately equal groups of COCs from abattoir-origin ovaries were washed and incubated for 1 h in minimum essential medium (MEM) with 10% equine serum. One group was incubated in 10(7) cell culture infective doses (50% endpoint) of BVDV for 1 h, while the other was incubated without virus. Subsequently, the groups were processed separately with cumulus cells, which were present throughout IVM, IVF and IVC. Cleavage was evaluated at 4 d and development to morulae and blastocysts at 7 d of IVC. After IVC, groups of nonfertile and degenerated ova or morulae and blastocysts were washed or trypsin-treated, sonicated and assayed for virus. Cumulus cells collected at 4 and 7 d were also assayed for virus. Anti-BVDV antibody was found in serum used in IVM and IVC but not in other media. A total of 1,656 unexposed COCs was used to produce 1,284 cleaved embryos (78%), 960 embryos > or = 5 cells (58%), and 194 morulae and blastocysts (12%). A total of 1,820 virus-exposed COCs was used to produce 1,350 cleaved embryos (74%), 987 embryos > or = 5 cells (54%), and 161 morulae and blastocysts (9%). Rates of cleavage (P = 0.021), cleavage to > or = 5 cells (P = 0.026) and development to morula and blastocyst (P = 0.005) were lower in the virus-exposed group (Chi-square test for heterogeneity). No virus was isolated from any samples from the unexposed group. For the exposed group, virus was always isolated from 4- and 7-d cumulus cells, from all washed nonfertile and degenerated ova (n = 40) and morulae and blastocysts (n = 57) and from all trypsin-treated nonfertile and degenerated ova (n = 80) and morulae and blastocysts (n = 91). Thus, virus persisted in the system despite the presence of neutralizing antibody in IVM and IVC media, and both washing and trypsin treatment were ineffective for removal of the virus. Presence of virus in 4- and 7-d cumulus cells as well as in nonfertile and degenerated ova were good indicators of virus being associated with morulae and blastocysts.

Infectious agents in bovine embryo production: hazards and solutions

Infectious agents in systems for producing bovine embryos might reduce the number and quality of embryos generated, result in transmission of disease to recipients and offspring, or confound findings of research. Embryo-associated pathogens might also jeopardize human health when the goal of embryo production is creating transgenic animals intended to be a source of pharmaceuticals or organs. This paper addresses risks and resulting hazards of pathogen and microbial contaminant introduction into in vivo or in vitro embryo production systems. Additionally, methods for prevention and quality control are discussed.

Effect of bovine herpesvirus-1 or bovine viral diarrhea virus on development of in vitro-produced bovine embryos

In previous experiments, zona pellucida (ZP)-intact in vitro-produced (IVP) embryos incubated for 1 hr with 10(6.3) TCID(50)/ml bovine herpes virus-1 (BHV-1), 10(5.3) TCID(50)/ml cytopathic (CP) bovine viral diarrhea virus (BVDV) or 10(5.3) TCID(50)/ml noncytopathic (NCP) BVDV showed no signs of virus replication or embryonic degeneration. The aims of the present study were to investigate whether a prolonged presence (24 hr or 8 days) of 10(6.3) TCID(50)/ml BHV-1 or 10(5.3) TCID(50)/ml BVDV in an in vitro embryo production system affected the rate of cleavage and embryonic development of ZP-intact embryos, and to point out eventual causes of adverse effects. When virus was present in each step of an IVP system, significantly lower rates of cleavage and blastocyst formation of virus-exposed embryos were observed, in comparison with control embryos (P < 0.01). When embryos were only exposed to virus during the in vitro fertilization (IVF), the rates of cleavage and blastocyst formation were significantly affected. The introduction of BHV-1 or BVDV during in vitro maturation (IVM) or in vitro culture (IVC) resulted only in significantly lower rates of blastocyst (P < 0.01). In all experiments, virus replication was not detected in the embryonic cells. On the other hand, virus replication was clearly demonstrated in oviductal cells in the co-culture system, resulting in a degeneration of these cells. In an additional experiment, synthetic oviduct fluid (SOF) without somatic cells was used as an alternative culture system. Even when SOF-embryos were exposed to 10(6.3) TCID(50)/ml BHV-1 or 10(5.3) TCID(50)/ml CP, and NCP BVDV, the rates of blastocyst formation of the BHV-1-, CP-, and NCP BVDV-exposed embryos were not different from the unexposed control embryos, 23%, 24%, and 24%, respectively, vs. 27%. Taken together, it can be concluded that the virus-induced adverse effects on embryonic development in conventional co-cultures were due to changes in the embryonic environment caused by infection of oviductal cells.

Quantity and infectivity of embryo-associated bovine viral diarrhea virus and antiviral influence of a blastocyst impede in vitro infection of uterine tubal cells

In previous studies, bovine viral diarrhea virus (BVDV) remained associated with IVF embryos after viral exposure and washing. However, uterine tubal cells (UTC) were not infected when exposed embryos were washed and individually co-cultured with them. The objective of this study was to evaluate quantity and infectivity of embryo-associated virus and antiviral influence of a blastocyst as possible explanations for failure to infect the UTC in vitro. Morulae and blastocysts were produced in vitro and washed. A portion of the embryos were incubated for 2 h in medium containing 10(6) to 10(8) cell culture infective doses (50%, CCID50) of a genotype I, noncytopathic BVDV per milliliter and then washed again. Virus isolation was attempted on sonicated negative (virus unexposed) and positive (virus exposed) control embryo groups after washing. The influence of quantity and infectivity of embryo-associated virus was evaluated by transferring exposed, washed embryo groups (2, 5, and 10 embryos/group) or sonicate fluid of exposed, washed, sonicated embryo groups (2, 5, and 10 embryos/group) to cultures containing bovine UTC in IVC medium that was free of BVDV neutralizing activity. The antiviral influence of an embryo was evaluated by adding 1 to 10(5) CCID50 of BVDV to UTC in the presence or absence of a single unexposed blastocyst in IVC medium. After 2 d in co-culture, the UTC, IVC medium and washed embryos (when present) were tested separately for the presence of BVDV using virus isolation. Virus was isolated from sonicate fluids of all positive but no negative controls. Virus was not isolated from any UTC following 2 d of culture with virally exposed groups of intact embryos. However, virus was isolated from UTC cultured with sonicate fluids from some groups of 5 (60%) and 10 (40%) embryos. Infective virus also remained associated with some groups of 2 (20%), 5 (40%) and 10 (60%) intact embryos after 48 h of post-exposure culture. Finally, primary cultures of UTC were more susceptible to infection with BVDV in the absence of a blastocyst (P = 0.01). Results indicate that insufficient quantity and reduced infectivity of embryo-associated virus as well as an antiviral influence of intact IVF blastocysts may all contribute to failure of embryo-associated virus to infect UTC in vitro.

Uterine tubal cells remain uninfected after culture with in vitro-produced embryos exposed to bovine viral diarrhea virus

Bovine viral diarrhea virus (BVDV) has been isolated from washed and sonicated, in vitro-produced embryos, but the infectivity of BVDV associated with intact, developing, embryos has not been demonstrated. The objective of this study was to determine if a dose of BVDV infective for co-culture cells was associated with individual, developing embryos, following artificial exposure to the virus and washing. In 5 replicates, zona pellucida-intact, in vitro-produced embryos were assigned to a negative control embryo group, or were incubated in 10(5)-10(6) cell culture infective doses (50%, CCID50) per milliliter of a type I, noncytopathic (strain SD-1) BVDV for 2 h. Unexposed negative control embryos and exposed positive control embryos were washed, sonicated and assayed for BVDV using virus isolation with immunoperoxidase monolayer assay. Immediately or following cryopreservation, remaining virally-exposed, washed embryos were co-cultured individually with BVDV-negative cultures of bovine uterine tubal cells in a medium free of BVDV-neutralizing activity. After two days in culture, uterine tubal cells and embryos (including the zona pellucida) were separated and washed. The culture medium, uterine tubal cells and embryos were then assayed for BVDV. Bovine viral diarrhea virus was not isolated from any negative control embryo group, but was isolated from all positive control embryo groups. Although all uterine tubal cell populations were confirmed to be susceptible to BVDV, virus was never isolated from uterine tubal cells or embryos from post-exposure culture. In conclusion, although BVDV remains associated with washed in vitro-produced embryos, the virus associated with unsonicated embryos was not infective for uterine tubal cells in vitro.

The effect of high concentrations of cryoprotectants on the passage of bovine viral diarrhea virus through the zona pellucida of in vitro fertilized embryos

The effect of high concentrations of cryoprotectants on the passage of bovine viral diarrhea virus (BVDV) through the zona pellucida (ZP) of intact bovine embryos during the pre-freezing step of cryopreservation was investigated in a series of experiments. In vitro fertilized (IVF) embryos at the blastocyst stage were exposed to 10(6) TCID50 BVDV (non-cytopathic NY-1 strain) in a 30% suspension of either ethylene glycol, glycerol, DMSO, or 2 M sucrose in physiological saline for 10 min at 20 degrees C. Subsequently, the embryos were washed free of residual unbound viral particles, and the ZP of some embryos were removed by micromanipulation. Groups of ZP-intact embryos, ZP-free embryonic cells and their respective ZP were then tested separately for the presence of virus. The infectious virus was detected in association with 81% (17/21) of samples containing non-micromanipulated ZP-intact embryos which were exposed to the virus and cryoprotectants and then washed 10 times and in 83% (43/53) of the samples containing only ZP from micromanipulated embryos (P > 0.05). The virus was not found in the samples containing the corresponding embryonic cells of embryos exposed previously to the virus and cryoprotectants. It was concluded that the transfer of embryos from the isotonic PBS solution into a highly hypertonic cryoprotectant solution did not cause the passage of BVDV through ZP and its entry to embryonic cells.

Washing and trypsin treatment of in vitro derived bovine embryos exposed to bovine viral diarrhea virus

Gametes, somatic cells and materials of animal origin in media are potential sources for introducing bovine viral diarrhea virus (BVDV) into systems for production of IVF bovine embryos. Further, the efficacy of washing and trypsin treatment for removal of BVDV from IVF embryos is questionable. Washing and trypsin treatments recommended by the International Embryo Transfer Society for in vivo-derived embryos were applied to in vitro-derived, virus-exposed, bovine embryos in this side-by-side comparison of treatments. Embryos for the study were produced in a virus-free system in which follicular oocytes were matured and fertilized in vitro and presumptive zygotes were co-cultured with bovine uterine tubal cells for 7 d. A total of 18 trials was performed, 9 using a noncytopathic BVDV and 9 using a cytopathic BVDV. In each trial, 4 equal groups of 10 or less, zona pellucida-intact embryos/ova were assembled, including 2 groups of morulae and blastocysts (M/B) and 2 groups of nonfertile or degenerated ova (NFD). Each group was prewashed and exposed to 10(4) to 10(6) TCID50/mL of either noncytopathic (SD-1) or cytopathic (NADL) BVDV for 2 h. Following in vitro viral exposure, one group of M/B and one group of NFD were washed. The other groups of M/B and NFD were trypsin-treated. Both treatments were consistent with IETS guidelines. After in vitro exposure to noncytopathic BVDV and washing, viral assays of 100% (9/9) and 78% (7/9) of the groups of M/B and NFD ova, respectively, were positive. After in vitro exposure to cytopathic BVDV and washing, viral assay of 33% (3/9) of the groups of both M/B and NFD ova were positive. After in vitro exposure to noncytopathic BVDV and trypsin treatment, viral assay of 44% (4/9) of groups of M/B and 67% (6/9) of groups of NFD ova were positive. Finally, after in vitro exposure to cytopathic BVDV and trypsin treatment, viral assay of 22% (2/9) of the groups of M/B and 44% (4/9) of the groups of NFD ova were positive. Contingency table analysis, in which data was stratified by embryo type and virus biotype, was used to compare results. While a difference existed between results of the 2 treatments of groups of M/B within the noncytopathic biotype (P = 0.01, Mantel Haenszel Chi-square), no difference was observed between comparison of treatment between all groups in both biotypes (P > 0.05).

Noncytopathogenic bovine viral diarrhea virus (BVDV) reduces cleavage but increases blastocyst yield of in vitro produced embryos

The growing application of in vitro embryo production systems that utilize slaughterhouse tissues of animals of unknown health status conveys the risk of disease transmission. One pathogen of concern in this regard is bovine viral diarrhea virus (BVDV), and the objective of this study was to investigate the effect of BVDV on in vitro embryonic development. A bovine in vitro embryo production system was experimentally infected with BVDV at 2 stages: prior to in vitro maturation by incubating cumulus-oocyte complexes (COC) with virus (strain Pe515; titer 10(6.2) tissue culture infective dose (TCID)50/mL) or vehicle for 2 h, and then during in vitro culture by the use of BVDV infected granulosa cells. Exposure to BVDV throughout in vitro production reduced cleavage rates (P = 0.01) but increased (P = 0.05) the number of embryos that reached the 8-cell stage when expressed as a percentage of cleaved oocytes. Blastocyst yield was increased by the presence of virus when expressed as a proportion of oocytes (P = 0.0034) or of those cleaved (P < 0.0001). The percentage of total blastocyst yield on Days 7, 8 and 9 for the control and virus treatments was 20, 51, 29 and 29, 41, and 29%, respectively, indicating that the rate of blastocyst development was nonsignificantly faster in the virus-treated group (P = 0.06). These results indicate that the presence of non-cytopathogenic BVDV in an in vitro production system may reduce cleavage rates but allow those cleaved to develop to blastocysts at a higher rate.

Association of bovine embryos produced by in vitro fertilization with a noncytopathic strain of bovine viral diarrhea virus type II

In the first experiment, heifers were infected experimentally with bovine viral diarrhea virus type II (BVDV-type II, strain CD87; characterized by high morbidity and mortality). Subsequently, in vitro fertilized embryos were produced from oocytes collected on Day 4, 8, and 16 post infection. In a total of 29 heifers, the infectious virus was detected in 55% of the samples of the follicular fluid, in 10% of the oviductal cells, in 10% of the uterine flushes and in 41% of the in vitro fertilized embryos. The highest number of embryos associated with the virus was detected in the group of animals slaughtered on Day 8 post infection (58%). The amount of the virus (10(1.5-2.0) TCID50/mL) associated with the washed single embryos generated from oocytes of heifers 8 and 16 d post infection was sufficient for disease transmission by intravenous inoculation to the seronegative recipients (6/15). In the second experiment, uninfected oocytes were exposed in vitro to BVDV (10(5) TCID50/mL) in the maturation medium and then fertilized and cultured prior to viral assay. Virus was detected in 4 of 7 samples containing embryos but not in samples of embryos produced from the control group of uninfected oocytes. The presence of BVDV in the IVF system did not affect embryonic development in vitro. In conclusion, it appears that BVDV-type II has the ability to be transferred with oocytes through the IVF system, resulting in infectious embryos with normal morphological appearance which may have a potential for disease transmission.