Bovine virus diarrhoea virus, a cause of early pregnancy failure in the cow

Seroprevalence of and Associated Risk Factors for Bovine Viral Diarrhea in Dairy Cattle in and Around Nekemte Town, East Wallaga, Oromiya Regional State, Ethiopia

Bovine viral diarrhea virus (BVDV) is an important pathogen affecting dairy cattle all over the world by causing significant economic losses due to reproductive and respiratory problems, immunosuppressive effects, increased risk of morbidity, and calf mortality. A cross-sectional study was conducted from February 2021 to August 2021 to determine the seroprevalence of bovine viral diarrhea (BVD) and identify risk factors associated with its occurrence in and around Nekemte Town of Ethiopia. Blood samples were collected from 305 dairy cattle of 41 herds by using cluster-sampling method. All sampled animals were identified by their age, breeds, origin, parity, pregnancy status, and history of reproductive and respiratory problems. Competitive ELISA was used in the laboratory to detect the presence of antibodies in the serum. At the animal and herd level, descriptive statistics were utilized to assess the amount of BVDV viral antibody circulation, and multivariable logistic regression analysis was employed to detect potential risk variables. The result demonstrates 9.84% (95% confidence interval (CI): 6.49-13.18) and 28.52% (95% CI: 23.46-33.59) seroprevalence of BVDV antibody at individual and herd level, respectively. Abortion (odds ratio (OR) = 2.75; p = 0.019), retention of fetal membrane (OR = 3.33; p = 0.011), purchasing of animals (OR = 2.98; p = 0.017), and pregnancy (OR = 3.16; p = 0.019) were variables significantly associated with the seropositivity of BVDV. Herd size was found to be substantially linked with BVDV infection at the herd level (p = 0.009). These moderate seroprevalence of BVDV results indicate that the virus is widely spread among dairy cattle at various farms in and around Nekemte Town, hurting dairy farm production and productivity. To reduce the seroprevalence of this infectious agent, cows with a history of reproductive disorders should be tested, and new animals should be quarantined before being introduced into herds, and more research should be done to assess the impact of reproductive failure and other effects associated with this virus.

Learning and strategic imitation in modelling farmers' dynamic decisions on bovine viral diarrhoea vaccination

Considering human decision-making is essential for understanding the mechanisms underlying the propagation of real-life diseases. We present an extension of a model for pathogen spread that considers farmers' dynamic decision-making regarding the adoption of a control measure in their own herd. Farmers can take into account the decisions and observed costs of their trade partners or of their geographic neighbours. The model and construction of such costs are adapted to the case of bovine viral diarrhoea, for which an individual-based stochastic model is considered. Simulation results suggest that obtaining information from geographic neighbours might lead to a better control of bovine viral diarrhoea than considering information from trade partners. In particular, using information from all geographic neighbours at each decision time seems to be more beneficial than considering only the information from one geographic neighbour or trade partner at each time. This study highlights the central role that social dynamics among farmers can take in the spread and control of bovine viral diarrhoea, providing insights into how public policy efforts could be targeted in order to increase voluntary vaccination uptake against this disease in endemic areas.

To Vaccinate or Not: Impact of Bovine Viral Diarrhoea in French Cow-Calf Herds

Bovine viral diarrhoea (BVD) remains an issue despite control programs implemented worldwide. Virus introduction can occur through contacts with neighbouring herds. Vaccination can locally protect exposed herds. However, virus spread depends on herd characteristics, which may impair vaccination efficiency. Using a within-herd epidemiological model, we compared three French cow-calf farming systems named by their main breed: Charolaise, Limousine, and Blonde d’Aquitaine. We assessed vaccination strategies of breeding females assuming two possible protections: against infection or against vertical transmission. Four commercial vaccines were considered: Bovilis^®, Bovela^®, Rispoval^®, and Mucosiffa^®. We tested various virus introduction frequency in a naïve herd. We calculated BVD economic impact and vaccination reward. In Charolaise, BVD economic impact was 113€ per cow over 5 years after virus introduction. Irrespective of the vaccine and for a high enough risk of introduction, the yearly expected reward was 0.80€ per invested euro per cow. Vaccination should not be stopped before herd exposure has been decreased. In contrast, the reward was almost nil in Blonde d’Aquitaine and Limousine. This highlights the importance of accounting for herd specificities to assess BVD impact and vaccination efficiency. To guide farmers’ vaccination decisions against BVD, we transformed this model into a French decision support tool.

Screening of persistently infected cattle with bovine viral diarrhea virus on dairy farms by using milk tanker and bulk tank milk samples for viral RNA and viral-specific antibody detection

The objective of this study was to provide a screening scheme of persistently infected (PI) cattle on dairy herds by combining reverse-transcription polymerase chain reaction (RT-PCR) to detect bovine viral diarrhea virus (BVDV) in milk tanker samples and commercial enzyme-linked immunosorbent assay to detect BVDV antibodies in bulk tank milk. We conducted a pilot survey and regional survey targeting all dairy farms in Ibaraki Prefecture by using milk tanker and bulk tank milk samples to screen PI cattle. Farms with positive samples underwent a follow-up test to identify PI cattle. In the pilot study, all virus-positive samples in bulk tank milk were included in the positive milk tanker samples. The RT-PCR assay successfully detected BVDV at dilutions of 1:1,600 by using two PI cows' milk. In the regional survey, 5 of 79 milk tanker samples were virus-positive. The virus was detected in three PI lactating cows and one PI calf on three farms. Antibody screening using bulk tank milk samples revealed 15 of 363 samples were positive, and 12 of 348 farms were BVDV antibody-positive. Follow-up tests on one farm identified three PI calves. Thus, eight PI cattle on five farms were identified in this study. In conclusion, combining BVDV detection using milk tanker samples and antibody detection using bulk tank milk is a feasible and economical method to efficiently screen PI cattle and confirm the PI-free status among dairy herds.

Modelling the spread of bovine viral diarrhea virus (BVDV) in a beef cattle herd and its impact on herd productivity

Bovine viral diarrhea virus (BVDV) is a common pathogen of cattle herds that causes economic losses due to reproductive disorders in breeding cattle and increased morbidity and mortality amongst infected calves. Our objective was to evaluate the impact of BVDV spread on the productivity of a beef cow-calf herd using a stochastic model in discrete time that accounted for (1) the difference in transmission rates when animals are housed indoors versus grazing on pasture, (2) the external risk of disease introductions through fenceline contact with neighboring herds and the purchase of infected cattle, and (3) the risk of individual pregnant cattle generating persistently infected (PI) calves based on their stage in gestation. The model predicted the highest losses from BVDV during the first 3 years after disease was introduced into a naive herd. During the endemic phase, the impact of BVDV on the yearly herd productivity was much lower due to herd immunity. However, cumulative losses over 10 years in an endemic situation greatly surpassed the losses that occurred during the acute phase. A sensitivity analysis of key model parameters revealed that herd size, the duration of breeding, grazing, and selling periods, renewal rate of breeding females, and the level of numerical productivity expected by the farmer had a significant influence on the predicted losses. This model provides a valuable framework for evaluating the impact of BVDV and the efficacy of different control strategies in beef cow-calf herds.

Bovine Viral Diarrhea Virus Infections

Bovine viral diarrhea virus (BVDV) continues to be of economic significance to the livestock industry in terms of acute disease and fetal loss. Many of the lesions relating to BVDV infection have been well described previously. The virus is perpetuated in herds through the presence of calves that are persistently infected. Relationships between various species and biotypes of BVDV and host defenses are increasingly understood. Understanding of the host defense mechanisms of innate immunity and adaptive immunity continues to improve, and the effects of the virus on these immune mechanisms are being used to explain how persistent infection develops. The noncytopathic biotype of BVDV plays the major role in its effects on the host defenses by inhibiting various aspects of the innate immune system and creation of immunotolerance in the fetus during early gestation. Recent advances have allowed for development of affordable test strategies to identify and remove persistently infected animals. With these improved tests and removal strategies, the livestock industry can begin more widespread effective control programs.

Changes in serum pregnancy-associated glycoprotein, pregnancy-specific protein B, and progesterone concentrations before and after induction of pregnancy loss in lactating dairy cows

Lactating crossbred dairy cows were synchronized to receive a timed artificial insemination (TAI), and blood samples were collected from all cows from TAI until pregnancy diagnosis 39 d after TAI (period 1), and from pregnant cows from onset of treatment until the end of the experiment (period 2). Cows diagnosed pregnant 39 d after TAI were randomly assigned to 1 of 3 treatments to receive (1) an i.m. injection of saline (CON, n=10); (2) an i.m. injection of PGF(2α) (PGF, n=10); or (3) an intrauterine infusion of 120 mL of hypertonic saline (INF, n=9). During period 1, serum pregnancy-associated glycoprotein (PAG) concentrations began to increase in pregnant cows by 25 d after TAI and differed from those in nonpregnant cows by 27 d after TAI, whereas serum pregnancy-specific protein B (PSPB) concentrations in pregnant cows differed from those in nonpregnant cows by 22 d after TAI. During period 2, time from treatment to cessation of the embryonic heartbeat was greater for PGF than for INF cows (36.0±5.7 vs. 0.2±0.1 h, respectively), and time from treatment to conceptus disappearance was greater for INF than for PGF cows (7.1±3.3 vs. 1.9±0.3 d, respectively). Overall, progesterone concentration was greater for CON and INF than for PGF cows (8.7±2.8, 8.2±3.1, and 1.0±2.3 ng/mL, respectively) due to luteal regression for PGF cows and corpus luteum maintenance for CON and INF cows. Serum PAG and PSPB concentrations differed among CON cows and PGF and INF cows beginning 1 and 2.5 d after treatment for PAG and PSPB, respectively. By 9.5 d after treatment, PAG and PSPB concentrations were similar to those of nonpregnant cows. We conclude that although timing of conceptus expulsion occurred 5.2 d later for INF than for PGF cows, serum PAG and PSPB concentrations decreased at a similar rate from the onset of treatment for both models of pregnancy loss evaluated.

Studies on BVD involving establishment of sentinel calves and assessment of herd immunity in a large dairy farm in Saudi Arabia

Little information is published, so far, regarding bovine viral diarrhea (BVD) in Saudi Arabia and the Gulf region. This study is the first of its kind in the country. Its aim was to explore the BVD situation in a large dairy farm, which has been experiencing reproduction problems suggestive of BVD virus infection, albeit the practice of routine vaccination. The study took two pathways; the first involved establishment of a cohort of sentinel calves so as: (a) to note the BVD virus activity in the farm by following the time lapse and pattern for waning of the maternally derived antibodies and detection of any subsequent seroconversion and (b) to look for any clinical signs suggestive of BVD virus infection in these calves. The second pathway was to assess the level of herd immunity in the different age groups of lactating cows and maiden heifers. The obtained results were discussed, and control strategies were outlined.

Selected diseases and conditions associated with bovine conceptus loss in the first trimester

The outcomes of insults to the bovine conceptus depend on the predilection of the insulting agent for the gravid reproductive tract, the virulence of the insult, and the developmental maturity/immune competence of the conceptus at the time of the insult. Agents that are lethal at one time during gestation may be harmless at another, or may have completely different effects (some not so harmless) at different gestational ages. This review discusses some of the known physical-mechanical, physiological, and infectious causes of first trimester bovine conceptus losses, including three infectious agents that have been the subject of recent studies for their potential to transmit disease via embryo transfer.

The cow in endocrine focus before and after calving

During the period 1 month before and 1 month after parturition in the cow, several events take place. The dam has to be prepared for the impending parturition and the uterus and ovaries must return to a certain stage to be prepared for a new pregnancy. Most of these processes are due to or reflected in endocrine changes. A special interest is of course the status of the foetus --"foetal well being". The processes could either be considered as normal in a clinical perspective or as impaired (dystocia, small calves, stillbirth, retained foetal membranes, etc.). The main question for this presentation is if normal and impaired performance could be mirrored in endocrine parameters. Many studies have been performed to follow endocrine changes during the periparturient period in the cow. The following parameters have been shown to be the most important and seem to be the most suitable for an endocrine supervision: Endocrine parameter: progesterone; parameter of: corpus luteum, maternal adrenals, placenta. Endocrine parameter: prostaglandin (PG) metabolite; parameter of: placenta, uterus, inflammation. Endocrine parameter: cortisol; parameter of: regulator of prostaglandin synthesis, stress. Endocrine parameter: free oestrogens; parameter of: placenta, ovaries. Endocrine parameter: oestrone sulphate; parameter of: placenta, calf weight. Endocrine parameter: pregnancy-associated glycoproteins (PAG); parameter of: placenta.

A model of the spread of the bovine viral-diarrhoea virus within a dairy herd

Wet BVDSim (a stochastic simulation model) was developed to study the dynamics of the spread of the bovine viral-diarrhoea virus (BVDV) within a dairy herd. This model took into account herd-management factors (common in several countries), which influence BVDV spread. BVDSim was designed as a discrete-entity and discrete-event simulation model. It relied on two processes defined at the individual-animal level, with interactions. The first process was a semi-Markov process and modelled the herd structure and dynamics (demography, herd management). The second process was a Markov process and modelled horizontal and vertical virus transmission. Because the horizontal transmission occurs by contacts (nose-to-nose) and indirectly, transmission varied with the separation of animals into subgroups. Vertical transmission resulted in birth of persistently infected (PI) calves. Other possible consequences of a BVDV infection during the pregnancy period were considered (pregnancy loss, immunity of calves). The outcomes of infection were modelled according to the stage of pregnancy at time of infection. BVDV pregnancy loss was followed either by culling or by a new artificial insemination depending on the modelled farmer's decision. Consistency of the herd dynamics in the absence of any BVDV infection was verified. To explore the model behaviour, the virus spread was simulated over 10 years after the introduction of a near-calving PI heifer into a susceptible 38 cow herd. Different dynamics of the virus spread were simulated, from early clearance to persistence of the virus 10 years after its introduction. Sensitivity of the model to the uncertainty on transmission coefficient was analysed. Qualitative validation consisted in comparing the bulk-milk ELISA results over time in a sample of herds detected with a new infection with the ones derived from simulations.

Effect of induction of late embryonic mortality on plasma profiles of pregnancy associated glycoprotein 1 in heifers

Inoculation with Actinomyces pyogenes and administration of prostaglandin (PG)F(2alpha) were used to induce late embryonic mortality (LEM) in heifers (n=8) on Days 30-38 of pregnancy in order to compare the profile for bovine pregnancy associated glycoprotein 1 (PAG1), progesterone and 15-keto-13,14-dihydro-PGF(2alpha) (PGFM). Two pregnant heifers were used as controls. Inoculation into the uterine body caused LEM, as established by ultrasonography in each heifer within 24h of treatment. When the inoculum was injected into the first part of the cervix, LEM occurred in one of two heifers (Heifer A) between 48 and 72 h after treatment. Similarly, PGF(2alpha) treatment caused LEM in three of four heifers. In six of eight heifers, PAG1 started to decrease steadily when it was accompanied by the subsequent death of the embryo. Inoculation through the cervix caused luteolysis in three of four heifers within 6-10 days after induction. After induction of LEM, PGFM concentrations showed a two to 3.8 fold increase in three of four heifers during the following six days, and from that time changed within normal ranges. The results of this study indicate that a PAG1 assay may provide an alternative method to ultrasonography for determining LEM in the cow.

Bovine viral diarrhoea virus infections and its control. A review

Infections with bovine viral diarrhoea virus continue to plague the cattle industry worldwide. The wish to control the negative effects of the virus has lead to the development of numerous vaccines, but also of eradication schemes. In this paper, a comprehensive overview on BVDV is given: the virus and its clinical manifestations, its occurrence and economic impact, the different routes of transmission, as well as diagnostic methods and objectives. Furthermore, the two major options for BVDV control--eradication and vaccination--are discussed as well as the risk for reintroduction of BVDV after eradication.

Pestivirus in cattle: experimentally induced persistent infection in calves

Twenty-two heifers were infected intranasally with non-cytopathic bovine viral diarrhoea virus (BVDV) between days 74 and 82 of pregnancy. All animals had developed serum antibodies against BVDV 5 weeks later. No clinical effects were seen in the heifers, and they all delivered a live calf. The newborn calves were generally small, appeared unthrifty as typical 'poor doers', and some developed secondary infections with diarrhoea and signs of respiratory disease. Eighteen of the 22 calves were born without antibodies against BVDV and were persistently infected (PI) with the virus. One was weak at birth and died the following day. Four calves were born with serum antibodies against BVDV and with no detectable virus. Three of these showed signs and/or pathological changes indicating disease in the central nervous system. Otherwise, there were no obvious clinical differences between these calves and the PI calves, nor were there any apparent significant differences in blood parameters between these groups. In general, the calves showed low gamma-globulin values and thrombocytopaenia, but moderately increased fibrinogen values and relatively normal lymphocyte numbers.

Insemination of susceptible heifers with semen from a non-viraemic bull with persistent bovine virus diarrhoea virus infection localized in the testes

Bulls shedding bovine viral diarrhoea virus (BVDV) in semen and simultaneously having a high concentration of circulating antibodies may cause reproductive problems and spread the viral infection within cattle populations. To investigate this in detail, three heifers were inseminated with BVDV-infected semen from a non-viraemic, seropositive Holstein-Friesian bull, named 'Cumulus'. One control heifer was inseminated with semen from a healthy bull that was free of BVDV. All four heifers remained clinically healthy throughout the experiment. The conception succeeded in the control animal and in two of the three heifers inseminated with semen containing BVDV. The heifer with the failed conception was the only one that became systemically infected with BVDV. This animal was deemed non-pregnant by ultrasonic examination on day 34 after insemination and showed no signs of subsequent oestrus during the entire experimental period. At slaughter, 42 days after insemination, there were no histopathological changes in the ovaries and virus was not detected in ovarian tissue. The fact that seronegative dams served with semen from persistently infected bulls have occasionally produced persistently infected calves together with the present findings and the fact that non-viraemic, seropositive bulls can constantly shed BVDV, suggest that the use of semen from such bulls in BVDV-free herds could have far-reaching consequences, especially if it led to the birth of persistently infected (P1) calves.

Time to first calving and calving interval in bovine virus diarrhoea virus (BVDV) sero-converted dairy herds in Norway

Dairy herds in Møre and Romsdal County, Norway (regarded as initially free from the bovine virus diarrhoea virus (BVDV) infection) were studied retrospectively from 1992 to 1996. The herd reproductive performance (time to first calving, calving interval, and number of breeding services) was investigated for a potential effect of BVDV sero-conversion. The herd culling pattern--possibly affecting the above measurements--was included for investigation. Two different statistical models were used: the generalised estimating equation (GEE) method and multilevel modelling using Gibbs sampling. Though slightly different estimates resulted, both models agreed on an effect of BVDV in the second year after sero-conversion on the herd average time to first calving by--on an average-- 14-16 days. In subsets of case herds testing positive for BVDV antibodies among young stock, the impact on time to first calving tended to be more pronounced by an additional increase of 18 days. No effect on the number of breeding services for heifers or cows was observed (indicating a need to search for other determinants than reduced conception risk). There appeared to be no effect of BVDV on the herd average calving interval. There was a tendency for a higher risk for reporting animals lost/died in sero-converted herds, which we believe might be related to the occurrence of mucosal disease.

Detection of viral antigen in placenta and fetus of cattle acutely infected with bovine viral diarrhea virus

The reproductive organs and fetuses of seven Norwegian Red heifers were investigated for the presence of bovine viral diarrhea virus (BVDV) antigen during the time of initial transplacental transmission of the virus. The heifers were inoculated with a noncytopathogenic BVDV at day 85/86 of gestation and were slaughtered at day 7, 10, 14, 18, or 22 postinoculation (pi). Cryostat sections of uterus, ovaries, placentomes, intercotyledonary fetal membranes, and fetal organs were examined using immunohistochemical techniques. A double immunofluorescence technique was used to identify cells that showed staining with antibodies against the leukocyte common antigen CD45 or the intermediate filament vimentin and BVDV antigens. The earliest stage of infection at which BVDV antigen could be detected in the fetuses was 14 days pi. At this stage, BVDV antigen was detected in cells of mesenchymal origin in the lungs and in large cells that morphologically resembled immature megakaryocytes in the liver. In the intercotyledonary fetal membranes and in the placentomes, BVDV antigen was not detected until 18 and 22 days pi, respectively. BVDV antigen was not detected in maternal tissue from any of the heifers. The present results indicate that fetal infection with BVDV can take place without preceding or simultaneous high concentrations of BVDV in uterus or placenta of acutely infected heifers.

Prevalence of antibodies to IBR and BVD viruses in dairy cows with reproductive disorders

We determined the prevalence of antibodies to infectious bovine rhinotracheitis virus (IBRV) and bovine viral diarrhea virus (BVDV) in sera of dairy cows on 4 different farms in the Republic of Croatia. A high percentage (60.8%) of cows had various reproductive disorders. The results showed that seroprevalence of infectious bovine rhinotracheitis (IBR) was 85.8% and that of bovine viral diarrhea (BVD) was 79.2% in tested cows. Antibodies to both viruses were found in 80.8% of cows with reproductive disorders but in only 46.8% of cows without reproductive disorders. This difference was statistically significant (P<0.01), and indicated a connection between reproductive disorders and simultaneous infections with IBR and BVD viruses in dairy cows.

The effect of bovine virus diarrhoea virus on reproduction in recently infected Norwegian dairy herds

A group of 32 dairy herds, recently infected with bovine virus diarrhoea virus (BVDV), was compared with a control group consisting of 75 BVDV free herds during a 3-year-period. Variables related to reproduction were registered. Results of multiple antibody examinations in bulk milk as well as samples of milk and blood from younger animals were used to select the herds. The incidence of abortions was statistically significantly different in the 2 groups, while the number of stillbirths, weak born calves, and congenital anomalies was not. Other variables such as percentage of non return, average number of inseminations per cow and calving interval showed during the study a trend to improve in the BVDV group, while they remained stable in the control group.

The duration of antibodies against bovine virus diarrhoea virus in bulk milk

Fifty-eight dairy herds, suspected to be recently infected with bovine virus diarrhoea virus (BVDV) due to a rise in BVDV antibodies in bulk milk, were followed over a two-year period. In 34 (59%) of these 58 herds (Group 1), pooled milk samples from heifers or pooled blood samples from calves were negative for BVDV antibodies. In this group as many as 53 and 76% of the herds again had antibody-negative bulk milk one and two years after the positive sample, respectively. Of the remaining herds, 5 and 17% had negative samples after one and 2 years respectively. Possible explanations for the limited duration of antibodies against BVDV in bulk milk are discussed. In 65% of the herds in Group 1, animals had been purchased and introduced into the herd, or the herds had been exposed to other forms of contact representing a risk of infection with BVDV. In the remaining 35% of the herds in this group, no explanation for the rise in BVDV antibodies in the bulk milk could be found. In this study the introduction of seropositive animals into the herd, and infection inducing seroconversion in one or more animals as the only result, seem to be the most probable explanations for the rise in antibody levels observed in Group 1.

The clinical manifestations of bovine viral diarrhea infection

BVDV infections may result in a wide range of clinical manifestations ranging from subclinical infections to a severe, highly fatal form referred to as MD. In recent years, a better understanding of pathogenesis has been achieved that has allowed for a better understanding of the different clinical forms of BVDV infection. Knowledge in this area continues to evolve. The clinical forms of BVDV infections are best understood by breaking them into categories that include infections in immunocompetent cattle, fetal infections, and infections in cattle that are immunotolerant to BVDV.

Pathogenesis of intrauterine infections with bovine viral diarrhea virus

BVDV shares with other Pestiviruses the ability to cross the placenta of pregnant host animals. The effects of fetal infections are complex and depend on a number of factors, e.g., age of the zygote/embryo stage, no infection seems to occur. During the last one third of gestation the infection is terminated by the ontogeny of the fetal immune system. This leaves a window of susceptibility during early stages of fetal development allowing establishment of viral persistence and/or the development of a number of fetopathologic effects. Additionally, fertility problems and abortions are observed. Calves that are born immunotolerant to BVDV and persistently viremic display a wide variety of abnormalities. However, there is an unknown proportion of calves born without any clinical signs indicative of persistent infection. The time of fetal infection during the first stages of pregnancy seems to play a crucial role with respect to the lesions induced. Generally, early infections seem to induce less damage compared with late infections, suggesting an indirect, possibly immune-mediated pathogenesis. Additionally, direct virus-cell interactions may play a role. Few data exist about the influence of differences in viral virulence on fetal pathology. Likewise the role of the viral target cell range is not clear.

Pharmacokinetics of flunixin and its effect on prostaglandin F2 alpha metabolite concentrations after oral and intravenous administration in heifers

Flunixin meglumine (FM) was administered either orally as granules or intravenously to six heifers in a two period crossover study. Single doses of 2.2 mg/kg body weight were used. Pharmacokinetic variables were calculated using statistical moment methods. The effect exerted by flunixin was measured as changes in the basal plasma concentration of the main metabolite of prostaglandin (PG) F2 alpha. After oral FM the arithmetic means of pharmacokinetic variables were: MRT = 12.7 h; MAT = 6.3 h; Cmax = 0.9 microgram/mL; tmax = 3.5 h. The bioavailability was 60% and the mean half-life (harmonic mean) was 6.2 h. Oral administration of FM inhibited as effectively as intravenous administration the prostaglandin biosynthesis. The concentration of the PG metabolite decreased almost as rapidly as after intravenous administration. The duration of the effect was prolonged and the PG metabolite concentration was significantly lower between 10 and 30 h after oral than after intravenous administration. The results indicate that oral dosing of flunixin, in the form of granules, can be an alternative to intravenous administration for therapeutic use in cattle.

Impact of bovine viral diarrhea virus on reproductive performance in cattle

The major economic impact of BVDV infections is in producing reproductive dysfunctions. The virus can have a detrimental impact on the developing fetus at all stages, but the most severe consequences occur early in gestation. The virus is maintained in the bovine population through the production of PI offspring. Only the NCB biotype of the virus can produce PI calves. The NCB biotypes is the one that produces the vast majority of BVDV infections and, as a consequence, the greatest economic losses. Biotype and antigenic variation are two independent variables and vaccines should emphasise antigenic composition, not biotype. A BVDV control program that does not emphasize heifers is doomed to failure.

Natural infection with bovine virus diarrhoea virus in a dairy herd: A spectrum of symptoms including early reproductive failure and retained placenta

The consequences of natural infections by bovine virus diarrhoea virus (BVDV) in a dairy herd comprising approximately 60 cows were studied over a 3 year period. The outcome of 39 pregnancies after artificial insemination or natural service during a 4 month period of risk for contracting BVDV was nine abortions, one mummified foetus, one still-birth, three calves that died within 1 week of age, 12 calves persistently infected (PI) with BVDV (11 males and one female) and 13 non-PI calves. Retrospective studies showed that only two of the 13 dams (15.4%) of non-PI calves had been inseminated once, which is a significantly (P < 0.001) lower rate than for 192 other gestations (66.7%) during the 3 year period.

The gestational duration of multiparous cows (but not of heifers) was longer (P < 0.01) for five cows with PI calves (mean ± SD 287.6 ± 9.5 days) than for 53 other gestations in 35 cows (280.6 ± 3.8 days). Five of the 12 dams of the PI calves had not expelled the foetal membranes within 2 days after calving, which is a higher (P < 0.001) incidence than the seven cases of retained placenta observed after 198 other calvings. Furthermore, there was a 4.4-fold higher risk (P < 0.01) of treatment for enteritis and/or pneumonia in calves and a 6.0-fold higher risk of calf mortality associated with the introduction of BVDV. The mean heart girth of the PI calves was less (P < 0.05) than that of non-PI calves, at both 80 and 180 days of age.

Plasma levels of prostaglandin F2 alpha metabolite and progesterone in repeat breeder heifers

A detailed clinical-endocrine investigation was performed in 6 repeat breeder heifers (RBH) with the aim being to ascertain whether endocrine asynchronism exists at luteal regression and during early pregnancy. The heifers were first studied during an open cycle and then after insemination when 3 heifers became pregnant. Circulating plasma levels of PGF2 alpha metabolite were measured every 2nd h, while progesterone (P4) levels were measured every 6th h. The oestrous period and intervals between the onset of oestrus and ovulation were relatively longer, compared with what is normally seen in heifers. Plasma levels of P4 at the onset of oestrus were higher than normal, but it was concluded that the plasma levels of PGF2 alpha metabolite and P4 in RBH at luteal regression and early pregnancy were normal.

Primary bovine viral diarrhoea virus infection in calves following direct contact with a persistently viraemic calf

Six calves, aged 24 to 58 days and not previously exposed to bovine viral diarrhoea virus (BVDV), were infected with this agent by nose-to-nose contact with a persistently BVDV viraemic calf. The study was conducted in two trials, using 3 calves in each. All 6 calves showed a peak interferon level in serum at 4 days post infection (dpi), and they seroconverted to BVDV at 16-21 dpi. The calves in trial 1 had diarrhoea for 2 or 3 days between 2 and 6 dpi and one calf again from 9 to 11 dpi. During the periods of fever, the calves were slightly depressed. Those in trial 2 were more depressed and their oral and nasal mucous membranes were reddened but they never had diarrhoea. In both trials, fever (up to 41.3 degrees C) was a prominent symptom at 8 to 9 dpi and 2 calves showed a diphasic fever course. Respiratory affection was mild and no medical treatment was required. Haematological assessment demonstrated a transient but significant leukopenia and lymphopenia at 4 dpi (P less than 0.01 and P less than 0.05 respectively) and 11 dpi (P less than 0.05 and P less than 0.01 respectively). A significant decrease in thrombocyte count was seen at 4 dpi (P less than 0.05, n = 3). This study has demonstrated that nose-to-nose contact is an effective way of transmitting BVDV from persistently infected to susceptible cattle.

Standing oestrus, ovarian function and early pregnancy in virgin and repeat breeder heifers

Seventeen virgin heifers (VH) and 14 repeat breeder heifers (RBH) were inseminated in spontaneous oestrus during a total of 86 oestrous cycles. Pregnancy was checked either by non-surgical embryo collections 14 or 17 days after ovulation or by real time ultrasonography 20-26 days after ovulation. The two categories of heifers were compared with respect to duration of standing oestrus, ovarian function and plasma progesterone levels after insemination and during early pregnancy. The results indicate that the duration of standing oestrus was longer in RBHs than in VHs. Ovulation disturbances occurred and were more common among the RBHs than among the VHs. Disturbances in the development of the corpus luteum were noted in both categories of heifers, the RBHs having less luteal tissue volume than the VHs. In general, plasma progesterone levels did not differ significantly between the two categories of heifers. Despite the strict control of oestrus and ovulation as well as additional AI when necessary in this study, a poorer pregnancy result for the RBHs than for the VHs was seen.

Lesions in aborted bovine fetuses and placenta associated with bovine viral diarrhoea virus infection

Abortions in dairy cattle were investigated on 55 dairy farms sited in North West England, using a multi-level diagnostic technique. After pathological examination of fetal and placental tissues collected at the time of abortion, possible causes for these abortions could be identified, supported by bacteriological and serological laboratory findings. Of 150 abortions investigated, Bovine Viral Diarrhoea (BVD) virus infection was related to 40 episodes (27% of the total), often accompanied by evidence of concurrent infections. Lesions associated with BVD abortions were found in fetal eyelid, lung, and occasionally myocardium. Lesions in the lung were most consistent, characterized by mononuclear inflammatory cell infiltration of peribronchiolar and inter-alveolar tissues. Placental lesions were non-specific. It is concluded that the lesions observed are insufficient to be the primary cause of abortion. However, the pathological changes associated with BVD infection in the placenta may allow secondary opportunist pathogens to cross the feto-maternal barrier, thereby threatening the health of the fetus and the physiological and endocrinological functions of the placenta which maintain pregnancy.