Establishment of a bovine leukosis virus-free dairy herd

A large dairy herd was established free of bovine leukosis virus (BLV) infection at the US Dairy Forage Research Center, Madison, Wis. Cattle introduced into the herd originated from BLV-infected herds, but only those negative for BLV antibodies by an agar gel immunodiffusion test were accepted there. Cattle that were found to be seropositive after their arrival at the new facility were promptly removed. Embryo transfer and artificial insemination were used to introduce new genetic stock into the herd. All recipients receiving embryos from BLV-positive donors and the 30 calves born from the successful transfers were seronegative at 21 months for BLV antibodies. Thus, under these conditions, embryo transfer and artificial insemination did not spread BLV. The agar gel immunodiffusion test was effective in screening cattle for BLV antibodies.     

Control of bovine leukosis virus in a dairy herd by a change in dehorning.

Following the demonstration that bovine leukosis virus was transmitted in calves by gouge dehorning, electrical dehorning at a younger age was implemented in a commercial Holstein herd. Subsequently, annual testing of the herd revealed a decline in the prevalence of bovine leukosis virus antibodies as older cattle dehorned by the former method were replaced by younger cattle dehorned by the latter method.     

Antibodies to bovine leukemia virus in a leukosis dairy herd and suggestions for control of the infection.

A closed herd of 765 Holstein-Friesian dairy cattle with a history of multiple cases of leukosis was tested for antibodies to bovine leukemia virus by the bovine leukemia-glycoprotein immunodiffusion test. A total of 355 animals (46.4%) were antibody positive. Prevalence was 60% in the 373 milking cows and 100% in the breeding bulls. Antibodies were present in 59% of newborn calves. Prevalence of antibodies was higher in older animals and cows in second lactation had a higher prevalence than cows in first lactation (72% vs 43%). Proposed control measures in this herd aim at preventing infection of calves, heifers and lactating cows by: 1) separating them into groups negative and positive for bovine leukemia virus antibodies, 2) not allowing calves to receive colstrum or milk from infected cows and 3) by using seronegative bulls for natural breeding tested at three month intervals. Calves should be tested after six months of age. Before this time calves of positive mothers should be treated as being positive.     

Evidence for transmission of bovine leukemia virus by rectal palpation in a commercial dairy herd

The risk of Bovine Leukemia Virus (BLV) transmission by rectal examination was determined over 22 months in a commercial dairy herd. All 167 BLV seronegative cattle, of breeding age or greater, were divided randomly into two groups and identified by neck-chain color. In the treatment group, routine rectal palpation occurred after a BLV infected animal and without a change of sleeve, while in the other group, palpation occurred in a similar manner with the exception that sleeves were changed between animals. When BLV seronegative cattle in either group were palpated after BLV infected cattle, the event and identification of the cattle involved were recorded. Serologic testing was performed eight times during the 22 month study to determine the number of animals that became infected following a palpation (an event). Thirty-one animals seroconverted during the study; 24 in the treatment (no sleeve change) group and seven in the sleeve change group. Sixteen of the animals in the treatment group that seroconverted had been palpated prior to their seroconversion. A hazard ratio (relative risk) for BLV seroconversion was determined between the two groups. Cows palpated with no sleeve change had a 2.8-fold increase in risk (confidence interval 1.1–6.8) of BLV infection. The increased risk of BLV infection associated with rectal palpation may have been affected by the presence of some highly infectious cows in the herd. This study confirms that rectal palpation without a change of sleeve may be a significant risk factor in some herds, and if efforts are made to decrease the spread of BLV in a herd, the potential for rectal sleeve transmission must be considered.     

Seroprevalence of bovine immunodeficiency-like virus and bovine leukemia virus in a dairy cattle herd.

To determine the prevalence of single vs. dual infection with bovine immunodeficiency virus (BIV) and bovine leukemia virus (BLV), sera (n = 95) from a dairy cattle herd were analyzed for anti-BIV and anti-BLV antibodies by an enzyme linked immunosorbent assay. Twenty-one percent (20/95) of samples were BIV-seropositive, while 52% (49/95) of the same samples were BLV-seropositive. A significantly greater percentage of BIV-seronegative samples were BLV-seropositive, 57% (43/75), than were BIV-seropositive samples, 30% (6/20). There was no significant correlation between data ranked from least to greatest amount of anti-viral antibody. Five cattle had persistent lymphocytosis (PL); all five were BLV-seropositive and two were BIV-positive. The mean anti-BLV titer was significantly greater in PL cattle, as compared at non-PL cattle, whereas there was no significant difference between the mean anti-BIV titer in PL cattle, as compared with non-PL cattle. These results provide additional information on the seroprevalence of naturally occurring BIV infection, and indicate that BIV can exist independent of other common infectious agents, such as BLV. Further, the results suggest that infection with BIV is not associated with an increased rate of infection with other infectious agents such as BLV.     

Seroepizootiologic study of bovine respiratory syncytial virus in a dairy herd

A 16-month seroepizootiologic study of bovine respiratory syncytial virus (BRSV) infection was conducted in a dairy herd. Results indicated that antibodies to BRSV present in serum from newborn calves were derived through the ingestion of colostrum. This passive immunity in calves became undetectable in an average of 99 days (SD = 36.5; range = 30 to 208 days). Two epizootics of respiratory tract disease occurred during the study period, and an association with BRSV was demonstrated in both epizootics. In the 2 epizootics, clinical signs of respiratory tract disease were only mildly to moderately severe, with no mortality or evidence of chronic pneumonia occurring. Seemingly, the passive immunity failed to protect calves from infection and disease caused by BRSV. Additionally, it was observed that if active immunity was induced by infection with BRSV, this immunity protected from the development of clinical disease, but not from reinfection upon subsequent exposures to BRSV.     

Concurrent malignant catarrhal fever and bovine virus diarrhoea virus infection in a dairy herd

An account is given of an outbreak of malignant catarrhal fever which occurred in a 98-cow dairy herd. Ten animals died or were slaughtered and the disease was confirmed by clinical and histological examination. Serological tests for malignant catarrhal fever virus were positive in three of four animals. The diagnosis of malignant catarrhal fever was complicated by the presence of bovine virus diarrhoea virus infection in three of the early cases. The initial cases of malignant catarrhal fever occurred in a group of nine-month-old calves which were housed in an old milking parlour with 19 pedigree Suffolk ewes at lambing time. Later cases occurred in two adult cows and in two heifers. Investigations of the remainder of the herd for evidence of bovine virus diarrhoea virus did not reveal the presence of any persistently infected cattle. Serological examinations for antibody to malignant catarrhal fever and bovine virus diarrhoea virus were carried out on the 19 Suffolk ewes. Six of them had neutralising antibody titres to malignant catarrhal fever virus and three were positive in the indirect immunofluorescence test. The possible roles of bovine virus     

Decreased periparturient transmission of bovine leukosis virus in colostrum-fed calves

BACKGROUND: The relation between calf bovine leukosis virus (BLV) infection status and colostrum ingestion is unclear. Two conclusions have been drawn from previous studies. One suggests that colostrum ingestion transmits BLV to neonatal calves. The second suggests that colostral antibodies are protective. HYPOTHESIS: Colostrum from BLV-positive cattle is protective in naturally exposed calves. ANIMALS: Twelve colostrum-deprived Holstein calves and 20 colostrum-fed Holstein calves born to BLV-infected cows. METHODS: Prospective study. Colostrum-deprived calves were tested weekly by enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) tests for BLV antibody and provirus for 12 weeks or until the animal became positive for BLV infection. Colostrum-fed calves were fed colostrum derived from BLV-positive cows. Thereafter, ELISA and PCR tests for BLV antibody and provirus were performed every other week until 2 consecutive negative ELISA tests or 1 positive PCR test was achieved. The proportion of calves that converted to BLV-positive status was calculated for each group and compared between groups by using the Fisher exact test. RESULTS: Four of 12 colostrum-deprived calves (33%) became BLV positive, whereas 0 of 20 colostrum-fed calves (0%) became BLV positive. The proportion of calves that became infected was significantly higher in the colostrum-deprived group (P = .014). CONCLUSIONS AND CLINICAL RELEVANCE: Calves born to BLV-positive cows are exposed during parturition, and a proportion of these calves will become infected with BLV. Administration of colostrum from BLV-positive cows greatly decreases the risk of infection.     

Disease in a dairy herd associated with the introduction and spread of bovine virus diarrhoea virus

In January 1982 an outbreak of diarrhoea among adult dairy cows in a closed herd of approximately 200 milking animals was shown to be caused by the introduction of bovine virus diarrhoea virus (BVDV). Affected animals showed a significant reduction in milk yield. One animal died and four were culled. Eight cows aborted and one weak calf was born. Of 121 calves born that year, 26 died, mostly from pneumonia, but five aged from three weeks to five months had enteric lesions of mucosal disease. Subsequent investigations of the whole herd in 1983 and 1984 showed that virus spread among the adults was slow and that BVDV continued to make a major contribution to calf losses. Again the greatest cause of loss was suppurative or fibrinous pneumonia. Overall, BVDV was isolated from 36 animals. Isolation of virus from a wide range of tissues of individual animals confirmed that they were viraemic at death. Viruses from calves dying of pneumonia and from aborted fetuses were non-cytopathic in tissue culture. Isolates showing varying degrees of cytopathogenicity were obtained only from tissues of one calf with a congenital neurological defect and the seven animals with enteric lesions consistent with a diagnosis of mucosal disease. Blood from all 89 BVDV antibody-free animals older than three months was tested for the presence of BVDV. Altogether, 12 calves were identified as persistently viraemic and all were apparently healthy when bled. Only two matured normally, four grew poorly and six died.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spread of bovine syncytial virus in a dairy herd over a two year period

During a two year period the spread of bovine syncytial virus was monitored in a closed herd of 50 to 100 milking cows. Out of a nucleus of 49 nonpregnant and pregnant heifers, six were found to be infected with bovine syncytial virus. Virus was detected only in the progeny of infected cows and not in the progeny of uninfected animals. Nineteen progeny of the bovine syncytial virus infected cows were studied in detail and virus was isolated from only four. Horizontal spread of the virus did not occur.     

Experimental transmission of bovine leukosis virus by simulated rectal palpation

Eight six-month-old Holstein male calves were experimentally inoculated by rectal palpation with whole blood from a donor seropositive to bovine leukosis virus. The inoculation consisted of the deposition of 2 ml of whole blood on a disposable obstetrical sleeve followed by a 30 second rectal palpation to simulate the process of pregnancy detection or artificial insemination. This procedure was repeated at weekly intervals for three consecutive weeks. All eight calves developed antibodies to bovine leukosis virus within five weeks after the initial palpation. The presence of the virus was demonstrated in the peripheral blood leucocytes of all eight calves at nine weeks. These results indicated that routine rectal palpation may be an effective mode of spread of bovine leukosis virus in susceptible cattle.     

Identification and eradication of bovine viral diarrhea virus in a persistently infected dairy herd.

A milking herd consisting of 55 Holstein cows had experienced abortions in several cows, as well as congenital malformations in 1 newborn calf. Bovine viral diarrhea virus was isolated from blood mononuclear cell samples obtained from several cattle, documenting 1 acute infection and 8 persistently infected carriers identified by clinical appearance and laboratory testing. Initial suspicion of persistently infected status in some, but not all animals, was facilitated by poor growth rates in some calves. Virus isolation was performed on transtracheal wash fluid obtained from acutely and persistently infected cattle with respiratory tract infection. We describe the measures taken to identify and characterize the infecting virus strain, and the series of actions taken to identify and eliminate persistently infected carriers in a herd experiencing several related problems that were shown to be caused by bovine viral diarrhea virus.     

Use of a polymerase chain reaction assay to detect bovine leukosis virus in dairy cattle

OBJECTIVE: To evaluate the use of a polymerase chain reaction (PCR) assay in detecting bovine leukosis virus (BLV) in adult dairy cows. DESIGN: Prospective study. ANIMALS: 223 adult dairy cows. PROCEDURE: Cows were tested for BLV status by use of an ELISA and a PCR assay. Sensitivity, specificity, predictive values of positive and negative tests, and the percentage of cows correctly classified by PCR assay were calculated. Ninety-five percent confidence intervals were calculated for sensitivity and specificity. RESULTS: Sensitivity and specificity were 0.672 and 1.00, respectively. Prevalence of BLV in this herd was 0.807. Predictive value of a positive test was 1.00, and predictive value of a negative test was 0.421. The percentage of cows correctly classified by PCR assay was 73.5%. CONCLUSIONS AND CLINICAL RELEVANCE: A positive PCR assay result provided definitive evidence that a cow was infected with BLV. Sensitivity and negative predictive value for PCR assay were low. Consequently, PCR assay alone is unreliable for routine detection of BLV in herds with high prevalence of the disease.     

Vertical transmission of bovine leukemia virus and bovine immunodeficiency virus in dairy cattle herds.

Vertical transmission of bovine leukemia virus (BLV) and bovine immunodeficiency virus (BIV) was investigated in five dairy cattle herds in Hokkaido, where 36.1 and 17.0% of cattle were BLV and BIV seropositive, respectively, and 9.9% of dams were co-infected with both BIV and BLV. Twenty six cases of offspring born from dams infected with only BLV (17 cases) or with both BIV and BLV (9 cases) were examined for the presence of BLV and BIV before and after colostrum feeding by polymerase chain reaction (PCR) and syncytium assay. After birth, all calves were separated immediately from their dams. The offspring born from BLV-positive dams were BLV-negative before colostrum feeding, suggesting that no transplacental transmission had occurred. Thereafter, these offspring were fed colostrum or milk from their dams, but still remained BLV-negative. The other offspring born from BLV-positive dams were fed with BLV-negative colostrum, or with pasteurized BLV-positive colostrum. All these calves remained negative for BLV infection, suggesting that in utero transmission of BLV is negligible. In the case of offspring born from dams co-infected with BLV and BIV, calves were BIV-positive before colostrum feeding at 1 day after the birth, indicating in utero transmission of BIV. After colostrum feeding from their dams, newborn calves became BLV-positive. In addition, one calf was BLV-positive even before colostrum feeding. These results suggest that BIV can be transmitted to offspring in utero, and that BLV can be transmitted through colostrum or milk if dams are infected with both BIV and BLV.     

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.     

Some observations on the epidemiology of bovine leucosis virus infection in a large dairy herd

Bovine leucosis infection rates were calculated for two years in a naturally infected dairy herd in which serologically positive animals were not preferentially culled. Transmission of infection was found to occur mainly during the winter housing period. No variation in susceptibility to infection with age was found and young animals did not show a prolonged time from infection to sero-conversion.