Factors associated with in utero or periparturient transmission of bovine leukemia virus in calves on a California dairy.

A three-year prospective study involving 143 calves born from infected cows was undertaken on a California dairy to evaluate possible factors of the dam associated with bovine leukemia virus infection in utero or during the periparturient period. In utero or periparturient infection occurred at a rate of 4.8% and was more likely in calves born to cows with an average peripheral blood lymphocyte count during pregnancy greater than 12,000 cells/microL (p = 0.043) or in calves born to cows that developed malignant lymphoma (p = 0.00004), but not in calves born to cows with p-24 antibodies (p = 0.675).     

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.     

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.     

Rectal palpation and transmission of bovine leukemia virus in dairy cattle.

To determine whether rectal palpation, using common obstetrical sleeves, serves as a mode of transmission of bovine leukemia virus in dairy cattle, field studies were conducted at 2 dairies. At a commercial dairy, significant difference was not observed in rate of seroconversion in heifers and cows in which the same sleeve or new sleeves were used for palpations. At a university dairy, where cattle were used to teach dairy husbandry and veterinary procedures, significantly (P less than 0.02) greater rate of seroconversion was observed in heifers and cows palpated with unwashed common sleeves than that observed in heifers and cows palpated with sleeves washed between use. Although rectal transmission of bovine leukemia virus under field conditions was documented, it was related to frequency of palpation and age of cattle.     

Protection of colostral antibodies against bovine leukemia virus infection in calves on a California dairy.

A three-year prospective study involving 244 calves was undertaken on a California dairy to evaluate the protective role of colostral antibodies against bovine leukemia virus (BLV) infection in calves. Calves were followed from birth to the time they left their individual hutch (TLIH), at about 90 days of age. The probability of being infected at TLIH and the daily risk of infection between birth and TLIH were modelled using the logistic and the Cox models, respectively. Calves with no detectable antibodies during the first week of life were up to 2.00 and 2.75 times more likely to be infected at TLIH compared to calves with low and high concentrations of antibodies during the first week of life, respectively (p = 0.01). When the daily risk was modelled, calves without antibodies at the estimated day of infection were up to 3.4 and 11.6 times more likely to become infected than calves with low and high concentrations of antibodies on that day, respectively (p less than 0.001). Results indicated that calfhood infection may be reduced by about 45% through the feeding of colostrum with BLV antibodies. Further reduction in infection may be possible by feeding calves milk powder, milk replacer, and/or milk from noninfected cows. Results also indicated that quantification of the effect of a time-dependent risk factor, such as colostral antibody concentration, might be affected if treated as a fixed factor.     

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.     

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 virus and bovine leukemia virus in dairy and beef cattle in hokkaido

Serological survey of bovine immunodeficiency virus (BIV) and bovine leukemia virus (BLV) infection was conducted in dairy cattle from 10 different regions of Hokkaido, Japan. Among 390 cattle, 11.0% of cattle were BIV-seropositive and 3.3% were BLV-seropositive. Moreover, in two dairy farms, where bovine leukosis has been reported, prevalence of BIV infections were 6.4 and 9.1%, respectively. In contrast, among 150 beef cattle, 16.6% were BIV-seropositive while none was BLV-seropositive. Dual infections with BLV and BIV in dairy cattle were tested by using 107 BLV-seropositive sera, and 20 sera were found BIV-positive (18.7%). These results indicate that BIV infection was widespread in Hokkaido.     

Descriptive epidemiology of postnatal bovine viral diarrhea virus infection in intensively managed dairy heifers.

OBJECTIVE: To evaluate risk of bovine viral diarrhea virus (BVDV) infection between birth and 9 months of age for dairy replacement heifers raised under typical dry-lot management conditions. DESIGN: Longitudinal observational study. ANIMALS: 446 calves. PROCEDURE: Calves were randomly selected from 2 dairies that used killed and modified-live BVDV vaccines. Repeated serologic and BVDV polymerase chain reaction assays were used to estimate risk of BVDV infection in calves of various ages (1 to 60 days; 61 to 100 days; 101 days to 9 months) and to estimate overall infection rate by 9 months of age. RESULTS: Risk of BVDV infection increased with age (maximum risk, 150 to 260 days). Proportion of calves infected with BVDV by 9 months of age was higher for dairy A (0.665), compared with dairy B (0.357). Percentage infected with BVDV type I did not differ between dairy A (18.2%) and dairy B (15.2%), whereas percentage infected with BVDV type II for dairy A (50%) was twice that for dairy B (21%). Between 210 and 220 days of age, infection with BVDV regardless of type was > 1.3%/d on dairy A and 0.5%/d on dairy B. CONCLUSIONS AND CLINICAL RELEVANCE: Under dry-lot conditions, a considerable amount of BVDV infection may occur before 9 months of age. Risk of infection increases with age. Although dairies may appear to have similar management practices, there can be considerably different risks of BVDV infection among dairies.     

Possible effect of altered management practices on seroprevalence of bovine leukemia virus in heifers of a dairy herd with history of high prevalence of infection.

A bovine leukemia virus (BLV) control program was instituted at a high-prevalence, purebred Holstein dairy. The specific control program required single use of needles and obstetrical sleeves, disinfection of tattoo equipment before use, dehorning by use of electrical burning devices, replacement of whole milk feeding with high-quality milk replacer, and heat treatment of colostrum before feeding. The effect of the program was estimated by comparing the pre- (1987) and postintervention (1989) prevalences of BLV-agar gel immunodiffusion titers within particular heifer age cohorts (0 to 90, 91 to 180, 181 to 360 days, and 361 days to parturition). Random serologic testing was conducted quarterly within each cohort, but was analyzed on a combined yearly basis. Seroprevalence of BLV decreased in all age cohorts greater than 180 days old, with significant decreases in the 361 days to parturition (P = 0.003) and the combined 181 days to parturition cohorts (P = 0.0004). Prevalence within the latter cohort decreased from 0.44 in 1987 to 0.17 in 1989. These results were obtained without either culling or segregation of BLV-agar gel immunodiffusion-positive cattle.     

Rectal transmission of bovine leukemia virus in cattle and sheep

Bovine leukemia virus (BLV) was transmitted by rectal inoculation of BLV-infective whole blood into cattle and sheep. Two cows and 2 sheep each were given 500 ml and 50 ml of blood, respectively, by rectal infusion. Two sheep which served as positive controls each were given 1 ml of the same blood, IV. All animals became seropositive to BLV by postinoculation week 5. Although relatively large volumes of blood were used for rectal inoculation, a base line for infectivity was established for the rectal route.     

Economic implications of bovine leukemia virus infection in mid-Atlantic dairy herds

OBJECTIVE: To determine the baseline costs of bovine leukemia virus (BLV) infection, including costs of clinical disease and subclinical infection, in a dairy herd representative of the mid-Atlantic region and compare these costs with the cost of a test-and-manage BLV control program. DESIGN: Stochastic spreadsheet model. SAMPLE POPULATION: A commercial Holstein dairy herd with 100 milking cows. PROCEDURES: A spreadsheet model was developed. The overall cost of infection included the cost of clinical disease (ie, lymphosarcoma [LS]) and the effects of subclinical infection on milk production and premature culling. Model input values and distributions were designed to reflect economic conditions in the mid-Atlantic region. Relative costs of infection and control were calculated for infection prevalences of 20, 50, and 80%. RESULTS: Estimated mean cost to the producer per case of LS was 412 dollars; for a herd with a 50% prevalence of BLV infection, annual incidence of LS was 0.66. Mean annual cost of subclinical infection at a 50% prevalence of infection was 6,406 dollars. Mean annual cost of a test-and-manage control program was 1,765 dollars. The cost of clinical disease and subclinical infection varied substantially with the prevalence of infection, whereas the cost of control varied with herd size. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that a basic BLV control program may be economically beneficial in herds in which the prevalence of BLV infection is > or = 12.5%. Farm-specific considerations may factor prominently when weighing the costs and benefits of an individual BLV control program.     

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.     

Prevalence of brucellosis and infectious bovine rhinotracheitis in organized dairy farms in India

This study was carried out to investigate the prevalence of bovine brucellosis and infectious bovine rhinotracheitis (IBR) in organized dairy farms with history of abortion in India. ELISA and Rose Bengal Plate Test (RBPT) were used to detect the seropositive animals and the test results indicated that 22.18% and 13.78% animals were declared as sero-positive by ELISA and RBPT, respectively. Milk Ring Test (MRT) was carried out only in one farm and 12.82% of the tested animals were turned positive. Culture examination analysis of milk samples, two animals revealed the presence of organisms indistinguishable from Brucella spp. The organism was confirmed as brucella by morphological characteristics and biochemical tests. An overall sero-prevalence of antibodies against IBR was found to be 60.84%. None of the genital and nasal swab samples was found to be positive for presence of bovine herpesvirus -1 (BHV-1) on repeated passage in Madin-Darby Bovine Kidney (MDBK) cell lines. Brucella and IBR considered as the causal agent for abortions in these farms. The present study indicates the urgent need and the necessity for control of these infectious diseases which cause heavy economic losses to the organized farms.     

Evaluation of a new antibody-based enzyme-linked immunosorbent assay for the detection of bovine leukemia virus infection in dairy cattle.

The objective of this study was to validate a new blocking enzyme-linked immunosorbent assay (ELISA) (designated M108 for milk and S108 for serum samples) for detecting bovine leukemia virus (BLV) infection in dairy cattle. Milk, serum, and ethylenediaminetetraacetic acid-blood samples were collected from 524 adult Holstein cows originating from 6 dairy herds in Central Argentina. The M108 and S108 were compared with agar gel immunodiffusion (AGID), polymerase chain reaction and a commercial ELISA. Because there is currently no reference test capable of serving as a gold standard, the test sensitivity (SE) and specificity (SP) were evaluated by the use of a latent class model. Statistical inference was performed by classical maximum likelihood and by Bayesian techniques. The maximum-likelihood analysis was performed assuming conditional independence of tests, whereas the Bayesian approach allowed for conditional dependence. No clear conclusion could be drawn about conditional dependence of tests. Results with maximum likelihood (under conditional independence) and posterior Bayes (under conditional dependence) were practically the same. Conservative estimates of SE and SP (with 95% confidence intervals) for M108 were 98.6 (96.7; 99.6) and 96.7 (92.9; 98.8) and for S108 99.5 (98.2; 99.9) and 95.4 (90.9; 98.1), respectively. The ELISA 108 using either milk or serum to detect BLV-infected animals had comparable SE and SP with the official AGID and a commercial ELISA test, which are currently the most widely accepted tests for the serological diagnosis of BLV infection. Therefore, ELISA 108 can be used as an alternative test in monitoring and control programs.     

Seroprevalence and associated risk factors of bovine brucellosis in Addis Ababa dairy farms

A cross-sectional study was carried out on bovine brucellosis in Addis Ababa dairy farms from November 2003 to April 2004. A total of 1,202 blood samples were collected from non-vaccinated, cross-bred dairy cattle. The Rose Bengal plate test (RBPT) was used as a screening test. Those serum samples reacting positively to RBPT were subjected to the complement fixation test (CFT) for confirmation. The RBPT detected 30 of 1,202 (2.5%) of the samples as brucellosis positive. The positive sera when further retested using CFT, 18 out of the 30 RBPT positive sera were confirmed to be positive. The prevalence of brucellosis based on CFT in the study area was 1.5%, and all positive sera were from female cattle. Result of the questionnaire survey revealed that percentage of 4.4% abortion and 9.5% retained fetal membranes. Abortion and retained fetal membranes were associated with Brucella antibodies (P?相似文献   

Control of bovine leukemia virus infection in dairy herds by agar gel immunodiffusion test and segregation of reactors.

Canadian cattle intended for export, in future, may have to originate from herds which are serologically negative for bovine leukemia virus, in addition to being negative individually by the agar gel immunodiffusion test as currently required. In this study, agar gel immunodiffusion testing of herds and segregation of reactors were examined. The results demonstrated that bovine leukemia virus infection could be controlled when three groups: 1) bovine leukemia virus-positive, 2) bovine leukemia virus-negative and 3) replacement cattle were maintained at separate locations.     

Disease management of dairy calves and heifers.

This article focuses on the most important diseases of dairy calves and heifers and presents clinical approaches that can improve detection, diagnosis, and treatment of herd-based problems. A systematic herd investigation strategy is pivotal to define the problems, understand important risk factors, develop a plan, and make recommendations for disease management accurately. A review of records, colostrum and feeding routines, housing and bedding management, routine procedures, vaccination, and treatment protocols begins the investigation and determines which diagnostic procedures and testing strategies are most useful. Disease management is most effective when the problem source is well defined and the exposure can be limited, calf immunity can be enhanced, or a combination of both. Screening examinations performed regularly or done at strategic time points improves detection of disease, can be used to monitor treatment outcomes, and can avoid disease outbreaks.