Shorter-term risk of Mycobacterium bovis in Irish cattle following an inconclusive diagnosis to the single intradermal comparative tuberculin test

In Ireland, new cases of bovine tuberculosis (bTB) are detected using both field and abattoir surveillance (More and Good, 2006). Field surveillance is conducted through annual testing of all cattle using the single intradermal comparative tuberculin test (SICTT). An animal may be deemed a 'standard inconclusive reactor' (SIR) to the SICTT if the bovine response is >2mm and between 1 and 4mm>the avian response. The herdowner then has three choices for the management of the SIR: option 1 is to have the animal retested after a minimum period of 42 days (an inconclusive reactor retest, IRR), option 2 is to slaughter the SIR and, provided the animal has no visible lesions, have a full herd test 42 days after the SIR leaves the herd, option 3 is to slaughter the SIR and have the lymph nodes examined using histology and/or culture for bTB. In the current study, we examine the bTB risk for SIRs both at slaughter prior to the IRR and at the IRR, and the future bTB risk of TIR animals (so-called 'transient SIRs'; SIR animals with a negative SICTT result at the subsequent IRR) that moved from the herd of disclosure within 6 months of the IRR. We also investigate factors associated with the future bTB status of SIRs at slaughter prior to the IRR and at the IRR. The study population included all SIRs identified in Ireland between 2005 and 2009 inclusive in a herd otherwise Officially TB free (OTF). Between 11.8% and 21.4% of SIRs slaughtered prior to the IRR were confirmed bTB positive at post mortem (using histology or culture if histology was not definitive), compared to 0.13-0.22% of SICTT -ve cohort animals. The post mortem bTB lesion rate of SIRs is lower than the lesion rate reported for reactor animals between 2005 and 2009 of between 34% and 39%, reflecting the doubtful infection status of these animals. Between 20.3% and 27.9% of herds were restricted at the IRR. The herd restriction rate amongst the national herd between 2005 and 2009 varied from 5.09% to 6.02%. TIRs that moved out of the disclosing herd within 6 months of the IRR were 12 times more likely to be bTB positive at the next test/slaughter compared to all animals in the national herd. The same increased risk did not apply to the SICTT -ve cohort animals that moved out of the same herds at the same time. Based on a range of measures, SIRs and TIRs are each at increased bTB risk into the future. Consequently, differential treatment of TIR animals would be justified.     

Evaluation of single reactor bovine tuberculosis breakdowns based on analysis of reactors slaughtered at an Irish export meat plant

The 'Singleton Protocol' was adopted by the Irish Department of Agriculture Fisheries and Food (DAFF) in 1996 to address the incomplete specificity of the single intra-dermal comparative tuberculin test (SICTT) used in Ireland for the detection of animals infected with bovine tuberculosis (bTB). The protocol allows the early restoration of disease-free status to herds with a single reactor breakdown, where the herd was not confirmed as infected with Mycobacterium bovis by epidemiological investigation, by postmortem examination or by further test. The current study examines the ability of the Singleton Protocol to identify false-positive reactors. It investigates the subsequent herd-reactor rate following single reactor removal and analyses the factors leading to a positive postmortem lesion outcome and a positive reactor retest result. Postmortem lesion results were obtained for 371 reactor animals from single reactor breakdowns that were killed at an export meat plant over a 19-month period. Epidemiological and test data for these animals and their herds were obtained from DAFF databases and analysed by univariate and multivariate statistical analysis. Singleton candidates had an 18.7 per cent lower lesion rate than single animal breakdowns not meeting the singleton criteria. No significant difference was found between Singletons and non singletons in the subsequent reactor retest results. Skin thickness at the SICTT is the most significant determinant of a positive lesion result. The area bTB history was shown to be a significant variable in producing a positive reactor retest result.     

Patterns of delayed detection and persistence of bovine tuberculosis in confirmed and unconfirmed herd breakdowns in cattle and cattle herds in Great Britain

Approximately 1500/6000 cattle farms that were depopulated during the foot and mouth epidemic in GB in 2001 had been repopulated and subjected to two unrestricted (herd considered free from bovine tuberculosis (bTB)) herd tests. Factors associated with herd breakdown(s) (HBD) and individual cattle reactor status at the second test were investigated. There were 96 HBD in total, with a 3-fold increased risk of HBD in herds that had had a HBD at the first test after restocking. Two mixed effect models were used to investigate factors associated with 324/246,060 reactor cattle at the second bTB test; 228 reactors were at confirmed HBD and 96 at unconfirmed HBD; 253 (79%) reactors at the second test were present and test negative at the first test. In confirmed HBD, the odds of cattle reacting were higher if the restocked farm had a history of bTB before 2001 and if the source and restocked farms were high frequency tested (HFT) farms (routine bTB tests at ≥1 per 2 years). Reacting cattle were more likely to have been born on the restocked farm before the first test after FMD and less likely to have been purchased from a low frequency tested (LFT) farm (routine bTB tests at 3-4 year intervals) after the first test compared with a baseline of cattle purchased from a LFT farm before the first test. Unconfirmed HBD at the second test was more likely when the first test was a confirmed HBD and when there was a history of bTB in the restocked farm. In contrast to confirmed HBD, cattle purchased from a LFT farm after the first test were at increased risk of reacting at an unconfirmed HBD at the second test. We conclude that a farm history of bTB suggests persistence of bTB on the farm. Confirmed tests indicate exposure to bTB for some time indicated by the increased risk from HFT source and restocked farms and a farm history of bTB. The risks for reactors are related to the farm and herd and duration of exposure to these risks. Therefore, the spread of bTB to na?ve herds would be reduced if farmers only introduced cattle known not to have been in herds and on farms exposed to bTB. Management of bTB on farms with bTB is complicated because there is undisclosed infection in cattle and environmental contamination.     

Impact of the national full herd depopulation policy on the recurrence of bovine tuberculosis in Irish herds, 2003 to 2005

This study evaluated the impact of the Irish herd bovine tuberculosis (bTB) depopulation policy (depopulation, disinfection, contiguous testing and local badger removal where implicated) on the recurrence of bTB infection, by comparing the future risk in restocked herds following depopulation for either bTB or bovine spongiform encephalopathy (BSE) during 2003 to 2005. Each herd was assigned a 'previous bTB risk', based on bTB history during the five years before depopulation. Future bTB risk was estimated, using a multivariable Cox proportional hazard model for time-to-breakdown for each study herd, to identify risk factors associated with bTB. Future bTB risk varied significantly by reason for depopulation and previous bTB risk. Herds depopulated for bTB (by definition, at high bTB risk) were not significantly different from BSE herds with no or a low previous bTB risk. BSE herds with a high previous bTB risk were found to be at significantly greater future bTB risk. Herd bTB depopulation measures, as currently applied in Ireland, are shown to be effective in enabling herds to attain and retain bTB freedom following restocking. Based on the data presented, and consistent with current knowledge of the bTB epidemiology, local badger removal contributes to efforts to limit recurrence of bTB in Ireland.     

Risks for bovine tuberculosis in British cattle farms restocked after the foot and mouth disease epidemic of 2001

The foot and mouth disease (FMD) epidemic of 2001 was used to investigate herd breakdown (HBD) with bovine tuberculosis (bTB) in totally restocked herds of cattle. By August 2004, 2941 restocked cattle herds, with cattle movements from before and after 2001, had been tested for bTB for the first time since restocking. A total of 6% (177) of these herds broke down at the first bTB test. A binomial logistic regression model with HBD (at least one reactor bovine) at the first test after restocking as the outcome was used to investigate risks associated with HBD. The final model contained three risk factors. There was an increased risk for HBD in restocked herds with every log increase in herd size with an OR=1.38 (CI 1.16-1.64) to a maximum OR of 10.75. When there was a history of bTB on the restocked farm before 2001 the OR, with CI not including unity, were 5.92, 4.63, 3.8 and 2.9 for last HBD in 2000, 1999, 1998 and 1997, respectively, indicating a persistence in increased risk for restocked herds from farms with a history of HBD in the previous herd before restocking, i.e. a different population of cattle. Finally, for every log increase in the number of cattle purchased from herds with a greater than biennial frequency of testing for bTB in the previous 8 years (i.e. perceived high risk herds for bTB) there was an OR=1.35 (95% CI 1.22-1.49). The maximum OR was 9.27. These results indicate that both introduction of bTB through the purchase of cattle from farms with a high perceived risk of bTB infection and persistence of bTB on the restocked farm, (not the farm's original herd), were associated with an increased risk of HBD in the newly formed herds after restocking.     

Differences in prevalence of tuberculosis in indigenous and crossbred cattle under extensive and intensive management systems in Tanga Region of Tanzania

A cross-sectional study was conducted between May 2003 and January 2004 on 130 households and 655 (246 indigenous and 409 crossbred) cattle to determine the prevalence of bovine tuberculosis (bTB) and assess risk factors associated with prevalence in smallholder dairy and traditionally managed herds in the Tanga region of North-eastern Tanzania. Random sampling, single intradermal tuberculin (SIT), comparative intradermal tuberculin (SCIT) tests and a questionnaire were used to gather individual animal and herd level information. From 642 animal tested by SIT, 35 (5.4%) were positive reactors for tuberculosis. Out of those 35 bTB positive reactors, eight (1.25%) proved to be positive reactors for tuberculosis upon further testing by SCIT. Based on the SCIT test, individual animal prevalences of bTB in the smallholder dairy and traditionally managed cattle was 2% and 0%, respectively. The corresponding overall herd prevalence was 5.7% and 0%, respectively. In conclusion, bTB prevalence seems low; however, its potential risk to public health is of concern; underscoring the need for further research, active surveillance to better understand the epidemiology of the disease in different cattle production systems in Tanzania.     

Evaluation of an O antigen enzyme-linked immunosorbent assay for screening of milk samples for Salmonella dublin infection in dairy herds.

Levels of antibodies to the O antigens (O:1,9,12) of Salmonella dublin were tested in 1355 serum, 1143 cow milk and 160 bulk milk samples from dairy herds using an enzyme-linked immunosorbent assay (ELISA). In order to define the background reaction, milk samples from all lactating cows and serum samples from 9 animals were collected in each of 20 salmonellosis-free herds located on the island of Bornholm, where cattle salmonellosis has not been reported. Similar samples were collected from all stalled animals in 10 herds with recent (< 6 months) outbreaks of salmonellosis located in Jutland, where salmonella infection is enzootic. Using herd history of salmonellosis, herd location and clinical status of the herds as criteria, the optimal cutoff in the milk ELISA was determined as being at least 5% of the samples having optical density > 0.5, resulting in herd sensitivity of 1.0 and herd specificity of 0.95. While none of the sera in the herds from Bornholm was ELISA positive, 2 herds had a few reactors in the milk ELISA. Using the same cutoff, all but 1 bulk milk sample from 150 herds on Bornholm was ELISA-negative, and all 10 salmonellosis-positive herds from Jutland were ELISA-positive. A significant correlation was found between ELISA reactions in milk and in serum of cows (34% and 32% respectively, rs = 0.69, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Impact of changes in cattle movement regulations on the risks of bovine tuberculosis for Scottish farms

Legislation requiring the pre- and post-movement testing of cattle imported to Scotland from regions with high bovine tuberculosis (bTB) incidence was phased in between September 2005 and May 2006 as part of efforts to maintain Officially Tuberculosis Free (OTF) status. In this analysis, we used centralized cattle movement records to investigate the influence of the legislative change on import movement patterns and the movement-based risk factors associated with new bTB herd breakdowns identified through routine testing or slaughter surveillance. The immediate reduction in the number of import movements from high incidence regions of England and Wales into Scotland suggests that pre- and post-movement testing legislation has had a strong deterrent effect on cattle import trade. Combined with the direct benefits of a more stringent testing regime, this likely explains the observed decrease in the odds of imported cattle subsequently being identified as reactors in herd breakdowns detected through routine surveillance compared to Scottish cattle. However, at the farm-level, herds that recently imported cattle from high incidence regions were still at increased risk of experiencing bTB breakdowns, which highlights the delay between the introduction of disease control measures and detectable changes in incidence. With the relative infrequency of routine herd tests and the insidious nature of clinical signs, past import movements were likely still important in determining the present farm-level risk for bTB breakdown. However, the possibility of low-level transmission between Scottish cattle herds cannot be ruled out given the known issues with test sensitivity, changes in import animal demographics, and the potential for on-farm transmission. Findings from this analysis emphasize the importance of considering how farmer behavioural change in response to policy interventions may influence disease transmission dynamics.     

Survey for antibodies to leukemia (C-type) virus in cattle.

Serums from 4,394 dairy cattle in 100 herds and from 2,794 beef cattle in 50 herds were tested for antibody to the bovine (C-type) leukemia virus (BLV), using the agar gel immunodiffusion test. Reactors were found in 66% of the dairy herds (10.2% of the cattle) and in 14% of the beef herds (1.2% of the cattle). The prevalence of reactors was examined with respect to age, herd size, and sex. Few of the reactors were less than 2 years old. There was a high percentage of reactors in small dairy herds (less than 50 cattle). In 22 dairy herds (1,354 cows and 96 bulls), the rate of infection in cows was compared with that in bulls. In those herds, 13.5% of the cows and 10.4% of the bulls were reactors.     

Breakdown severity during a bovine tuberculosis episode as a predictor of future herd breakdowns in Ireland

A retrospective cohort study of Irish cattle herds investigated whether the severity of a herd’s bovine tuberculosis (BTB) breakdown was a predictor of the hazard of a future BTB breakdown in that herd. Data on 10,926 herds not having had BTB in 1995 (the “non-exposed” group) were obtained using a 10% random sample from all herds without BTB in 1995. Data on 6757 herds that had a new BTB breakdown in 1995 (the “exposed” group) were obtained and categorized into five increasing exposure-severity classes based on the total number of standard reactors (to the single intra-dermal comparative cervical tuberculin test) detected during the breakdown. Exposed herds were deemed to be free of BTB after they passed a 6-month check test; non-exposed herds were deemed free as of the date of the first negative herd-test in 1995.

In the 5 years after 1995, 18% of the non-exposed herds had a BTB breakdown, whereas 31% of the exposed herds had a subsequent breakdown. Relative to the hazard for non-exposed herds, the hazard for the first future singleton standard reactor breakdown, was 1.6-times higher for exposed herds with only 1 standard reactor in 1995, and 1.8-times higher for those exposed herds with 4–8 standard reactors during the 1995 episode. When the outcome for future breakdowns was 2 or more standard reactors, the hazard ratios ranged from 1.6 for exposed herds with only 1 standard reactor in 1995 up to 2.9 in exposed herds with 8 or more standard reactors during the 1995 episode. The latter hazard ratio varied over time, decreasing to 1.7 after 3 years of risk. The hazard of a future BTB breakdown increased directly with number of cattle in the herd, a positive history of previous BTB in the herd, and the local herd prevalence of BTB. The presence of confirmed BTB lesions in reactor cattle was not predictive of the future breakdown hazard when the effects of other factors were controlled.     

Herd and individual animal risks associated with bovine tuberculosis skin test positivity in cattle in herds in south west England

The aim of this study was to investigate the cattle—exposure factors associated with the risk of a bovine animal reacting to a bovine tuberculosis (bTB) skin test at a whole herd test. There were 148 study farms enrolled. These were located in six counties of the south west of England in an area considered endemic for bovine tuberculosis (bTB): 24% were restocked after foot and mouth disease (FMD) in 2001; all farms were located within the Randomised Badger Culling Trial (RBCT) area. Data on cattle on these farms were sourced from the bTB Vetnet database from 1996 to 2004 and from the British Cattle Movement Scheme database. Individual animal records were created that included data on whether or not an animal became a reactor at a full-herd bTB test between 1 June 2001 and 19 August 2004, their prior exposure to cattle with bTB (defined by presence at a bTB test where at least one reactor was detected), whether the animal was homebred, the farm history of bTB and the farm restocking status. Data from 144 farms were used, 4 farms had no data.Cattle were more likely to react to the bTB skin test when they had been present at a previous bTB herd test (or tests) where other cattle had reacted to the skin test. This positively correlated with age and the number of bTB tests an animal had had. Cattle on restocked farms were less likely to react to the skin test compared with cattle on continuously stocked farms. These results highlight the likely importance of exposure to infected cattle at a previous test as a source of infection to cattle that subsequently became reactors and suggest that there was a lower risk of exposure to bTB to cattle in newly formed herds.     

Early removal of cows with Brucellosis and the effect in strain 19 vaccinated cattle herds

The effect of early removal of cows excreting pathogenic Brucella abortus following Strain 19 vaccination of beef cattle herds was determined by comparing cumulative incidence (CI) of brucellosis reactors post-vaccination (p.v.). Adult female cattle in six herds were tested, reactors removed, and vaccinated with 3×10⁹ colony-forming units of B. abortus Strain 19. Cattle were tested at 2 months p.v. and culture-positive cattle were removed from a principal cohort of three herds at approximately 3 months p.v., and removal from a control cohort of three herds delayed until approximately 7 months p.v. Neither CI nor time to eliminate brucellosis was significantly different between cohorts.A review of the parturition data revealed that more of the infected cows in the principal cohort herds terminated gestation before removal. These data suggest that stage of gestation plus diagnostic and management alternatives to prevent parturition of infected cattle in the herd are more important factors in herd plans than early removal of postparturient infected cows following whole-herd Strain 19 vaccination.     

Lungworm disease in dairy cattle: symptoms,diagnosis, and pathogenesis on the basis of four case reports

Clinical lungworm disease appears to occur frequently in Dutch dairy herds. Because the clinical diagnosis is difficult to make in adult cattle, the clinical diagnosis, laboratory diagnosis, differential diagnosis, therapy, and prevention are discussed in this article. In addition, four cases of lungworm disease in adult cattle are presented. The main clinical complaints were coughing, decreased milk production, and weight loss. Several lactating cows died in one herd. The disease history of four herds revealed that introduction of susceptible cows or heifers to herds with cows with subclinical patent lungworm infections had resulted in a pasture infection, leading to clinical problems in both the newly introduced and 'resident' cows of the herd. Further history analysis of the fourth herd revealed that re-introduction of lungworm infection by newly purchased cows in a lungworm free herd resulted in clinical lungworm problems in adult and young animals. The fourth case led to the conclusion that lungworm infection must have been re-introduced by cows purchased from another farm.     

A Cross-sectional Study of Bovine Tuberculosis in Dairy Farms in Asmara,Eritrea

Bovine tuberculosis in dairy cattle in Asmara, Eritrea, was studied using a cross-sectional study to describe its prevalence and to identify factors associated with it. A total of 72 randomly selected herds were included in the study. The comparative intradermal tuberculin test was used for the diagnosis. Of 1813 individual animals tested, 14.5% were reactors. Thirty herds (41.7%) had at least one reactor but, by defining a reactor herd as any herd with two or more reactors, only 19 (26.4%) herds were classified as reactor herds. Based upon individual animal specificity of 98.5%, the calculated herd specificity was >99%. A multiple logistic model showed that the presence of exotic breeds was associated with a high risk (odds ratio = 5.70; 95% confidence interval 1.13–28.8). An increased risk was also linked to large herds. Keeping the animals always indoors reduced the risk, but could not be fitted to the model owing to empty cells.     

Bovine tuberculosis in Europe from the perspective of an officially tuberculosis free country: trade, surveillance and diagnostics

Switzerland has been officially free of bovine tuberculosis (OTF) since 1960. Since 1980 the control of bovine tuberculosis (bTB) has been reduced to passive abattoir surveillance. Isolated cases of bTB, partly due to reactivation of human Mycobacterium bovis infections with subsequent transmission to cattle, have been noticed in the last years. In Europe, the overall prevalence of bTB is slightly increasing. Both OTF and non-OTF countries report increases in the proportion of bTB positive cattle herds. Current bTB eradication and control programs in Europe are facing a range of challenges. Whole herd depopulation is becoming a less attractive option for economic reasons and due to animal welfare concerns. Live animal trade is increasing both at national and international levels. Regarding these tendencies and taking into account the chronicity of bTB infection, pre-movement testing is becoming increasingly important as a central tool for eradication and for protection against re-introduction of bTB. Pre-movement testing, however specifically focuses on the infection status in individuals, requiring a high level of diagnostic accuracy to correctly diagnose infected animals. Current screening tests for bTB, however, have been designed to meet demands as herd tests. This illustrates that the modification of existing and/or the development of new diagnostics for bTB might be needed. The tuberculin skin test (TST), the primary screening test for bTB may in certain situations have low sensitivity. The interferon gamma (IFN-γ) assay is accepted to be more sensitive compared to TST. Reduced specificity, however, especially in areas of low bTB prevalence raises concerns. New antigen combinations including Rv3615c, OmpATb and others have been shown to complement ESAT-6 and CFP-10 in the whole blood IFN-γ assay and resulted in improved sensitivity (compared to ESAT-6 and CFP-10) and specificity (compared to tuberculins). Lesion detection after slaughter represents a cost-effective procedure for passive surveillance of bTB, especially in areas of low prevalence or in regions free of bTB; however, its sensitivity is very low. This illustrates that trade is linked with a certain risk to re-introduce bTB in OTF regions or countries and that there may be delays in detecting a re-introduction of bTB. In conclusion, regarding the fact that some parameters linked with bTB programs are changing, the development of improved diagnostic tests with a high reliability for use as individual animal tests will be important for future eradication of bTB, in line with international commitment to high standard animal health programs.     

Survey of Mycobacterium avium subspecies paratuberculosis serological status in beef herds on community pastures in Saskatchewan

Johne's disease is a well recognized problem in dairy herds. Relatively little information is available on either the prevalence or the control of Johne's disease in commercial cow-calf operations. In the fall of 1999, blood samples were collected during pregnancy testing from cows on community pastures in Saskatchewan. Sera from these cows were analyzed using a commercial ELISA for antibodies to Mycoplasma avium subspecies paratuberculosis. All cows from each herd examined at the community pastures were sampled. Of the 1799 samples tested, 15 had sample to positive (S/P) ratios greater than 0.25 and were considered positive (apparent sample prevalence, 0.8%; 95% CI, 0.4% to 1.5%). If we assume test sensitivity of 25% and specificity of 98% as recommended by the National Johne's Working Group, the true sample prevalence is not significantly different from 0.0%. The ELISA S/P results for the antibody test-positive animals ranged from 0.27 to 2.5. If a herd was classified as positive based on one test-positive animal, the average herd apparent prevalence was 15.2% (95% CI, 7.1% to 28.6%). If the potential for false-positive results was considered with 2 or more positive animals being required for positive herd status, the herd prevalence was 3.0% (95% CI, 0.4% to 13.4%). Because of the very low prevalence in cow-calf herds, future research to identify risk factors and control points should target problem herds and utilize a case-control study design.     

Evaluation of a bulk-milk ELISA test for the classification of herd-level bovine leukemia virus status

The results of a commercial bulk-milk enzyme-linked immunosorbent assay (ELISA) test for herd-level bovine leukemia virus (BLV) status were compared to results obtained from individual agar-gel immunodiffussion (AGID) testing on sampled cattle. A positive herd was defined as a herd having one or more AGID-positive animals. The estimated true herd status was based on the sensitivity and specificity of the AGID test and the number of cattle sampled per herd. Ninety-seven herds were used, with a mean of 13 cows sampled per herd. The AGID test indicated an apparent herd prevalence of 70.1%. After accounting for the number of cows sampled and the sensitivity and specificity of the AGID test, the estimated true herd prevalence of BLV was 52.3%. The ELISA test identified 79.4% of herds as positive for BLV, and had an apparent sensitivity and specificity of 0.97 and 0.62, respectively. However, after accounting for the sensitivity and specificity of the AGID test in individual animals, the specificity of the ELISA test was 0.44. The ELISA test was useful for identifying BLV-negative herds (i.e., ruling out the presence of BLV infection in test negative herds). With the moderately low specificity, herds identified as positive by the ELISA test would require further testing at the individual or herd level to definitively establish their BLV status.     

Neospora caninum serostatus and milk production of Holstein cattle

OBJECTIVE: To determine whether Neospora caninum serostatus was associated with milk production among Holstein cattle in Ontario. DESIGN: Case-control study and cross-sectional observational study. ANIMALS: 3,702 Holstein cows in 83 herds (case-control study) and 3,162 Holstein cows in 57 herds. PROCEDURE: Herds in the case-control study were grouped on the basis of N. caninum abortion status. Herds in the observational study were considered representative of Ontario dairy herds. The N. caninum serostatus of individual cows was determined with a kinetic ELISA. Milk production was modeled to compare seropositive with seronegative animals while controlling for parity, days since parturition, and herd clustering. RESULTS: In the case-control study, 305-day milk production of seropositive cows was significantly less than milk production of seronegative cows in herds with abortions attributable to N. caninum infection and in herds with abortions attributable to pathogens other than N. caninum, but not in herds without abortion problems. In the observational study, 305-day milk production for seropositive cows was not significantly different from milk production of seronegative cows. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the association between N. caninum serostatus and milk production in Ontario Holstein dairy cattle may depend on abortion status of the herd. In herds with abortion problems, regardless of cause, N. caninum-seropositive cattle produced less milk, whereas in herds without abortion problems, N. caninum-seropositive cattle produced the same amount of milk as seronegative cattle.     

Herd-level risk factors for infection with Mycobacterium paratuberculosis in US dairies and association between familiarity of the herd manager with the disease or prior diagnosis of the disease in that herd and use of preventive measures

OBJECTIVE: To evaluate associations among herd infection status, herd management practices, and familiarity of the herd manager with Mycobacterium paratuberculosis (Johne's disease) or prior disease diagnosis in that herd to support development of Johne's disease-control programs. DESIGN: Population-based cross-sectional study. SAMPLE POPULATION: 1,004 US dairies, each with > or = 30 cows, representing 79.4% of US dairy cows. PROCEDURE: Questionnaires were administered to dairy managers, and blood samples were collected from cows during herd visits. Sera were tested for antibodies to M paratuberculosis, using a commercially available ELISA. Multivariable logistic regression analyses were used to evaluate associations between use of management practices, herd disease status, and familiarity of the manager with Johne's disease or prior diagnosis of Johne's disease in that herd. RESULTS: Results from serologic testing revealed that 3.4% of cows and 21.6% of dairy herds were infected with M paratuberculosis. Factors associated with infection included number of cows in herd, region of country, percentage of cows born at other dairies, group housing for periparturient cows, and group housing for preweaned calves. Few preventive practices were positively associated with prior diagnosis of Johne's disease (time of separation of newborn calf from dam) or familiarity of the manager with the disease (teats and udder washed before colostrum collected). CONCLUSIONS AND CLINICAL RELEVANCE: Risk factors associated with Johne's disease in this study confirmed those management practices generally recommended for disease control. An educational problem, however, is the finding that herd managers familiar with Johne's disease generally use management practices similar to those used by managers unfamiliar with the disease.     

Bovine Leukosis II. Comparison of Hematological Classification with DNA Synthesis Between Herds

Blood samples of 126 mature cows with “persistent” hematological status from two leukosis herds and a leukosis free control herd were collected for determining hematological status and estimation of replicating lymphocytes. To quantitate the number of DNA synthesizing cells, the blood was incubated with tritiated thymidine in vitro followed by autoradiography. Classification of animals according to lymphocytosis status did not reveal clearly whether or not a difference existed between the two leukosis herds. The estimation of DNA synthesizing lymphocyte counts showed that the animals from the two leukosis herds did not differ from each other while differing significantly from control herd animals. The study suggests that the similarities between the two leukosis herds, while ambiguous on lymphocyte counts alone, become clear when DNA synthesizing cell counts are compared. Thus the animals of the two leukosis herds belonged to the same “leukosis” population.