Effect of a test and control program for Johne's disease in Victorian beef herds 1992-2002

OBJECTIVE: To report on progress in Johne's disease (JD) control in infected beef herds participating in the Victorian Johne's disease test and control program (TCP). PROCEDURE: Clinical histories and JD testing data recorded by the Department of Primary Industries were analysed for 18 beef herds participating in the TCP. The herds were required to conduct annual whole herd tests with an absorbed ELISA, cull reactors and control the grazing of young cattle to minimise infection. RESULTS: Testing of over 11,000 animals identified 68 reactors giving an average prevalence of reactors at the first whole-herd test round (T1) of 0.77%. There had been 20 clinical cases detected in the 7 years before the TCP started and two cases detected in the 10 years after TCP started. Most reactors and all clinical cases were born before the TCP started. Of 34 reactors necropsied, 25 (74%) were confirmed to have JD by histology or culture of tissues. The modal age of reactors and clinical cases was 5 and 6 years respectively. Six herds completed the program by achieving three successive negative whole herd tests, four herds dropped out and eight continued to test. There were 18 reactors detected at T1 and 33 reactors that were negative at T1 but detected at subsequent tests. CONCLUSION: The TCP was associated with a marked decline in clinical cases. The similar age distributions of clinical cases and reactors probably meant that testing detected animals for which clinical disease was imminent. Whether the measures used in the TCP were adequate to control the disease in beef herds could not be determined because of the long incubation period of the disease. The relatively high proportion of the reactors investigated that were confirmed as infected provided confidence that the test was continuing to operate at a high specificity. If all unconfirmed reactors were presumed to be uninfected, the minimum specificity of the ELISA was 99.83%. The sensitivity of the ELISA appeared to be very low because of the large number of reactors that were negative at T1 but positive at later tests.     

Characterization of Minnesota dairy herds participating in a Johne's disease control program and evaluation of the program risk assessment tool

The objectives of this study were to: (1) characterize Minnesota dairy herds participating in a Johne's disease control program (JDCP) based on herd size, milk production, and clinical Johne's disease (JD) history, (2) evaluate if change in farm management practices, expressed in risk assessment (RA) total score, is associated with the change between the first and most recent ELISA test herd seroprevalence or change in clinical JD culling rate, and (3) identify farm factors associated with ELISA seroprevalence. A total of 1234 RA, performed between January 2000 and February 2004, were available for analysis from 714 dairy herds. ELISA test results from herd sampling between 2000 and 2004 were obtained from the Minnesota board of animal health (MBAH) database, and were available for 474 herds. Both the first and the most recent ELISA test results for herds with more than one RA were available for 262 herds. Mean herd size and mean annual milk production per cow was higher in JDCP dairy herds (161 milking cows) than either all Minnesota dairy herds or Minnesota dairy herd improvement association (DHIA) herds. For herds with more than one RA available, the most recent RA total score was significantly lower (mean 11% less) than the first. The change in RA total score (and any RA subtotal scores) between the first and most recent RA was not associated with the change between the first and the most recent ELISA within-herd seroprevalence or the change in JD culling rate between the first and most recent RA. The most recent ELISA test results were positively associated with postweaned heifer score and JD culling rate. The RA score was not found to be an effective tool for the prediction of ELISA seroprevalence.     

Estimate of the sensitivity of an ELISA used to detect Johne's disease in Victorian dairy cattle herds

OBJECTIVE: To estimate the sensitivity of the ELISA used in dairy cattle herds participating in the Victorian Bovine Johne's Disease Test and Control Program (TCP). PROCEDURE: The percentage of ELISA reactors in age and test cohorts was estimated from age-specific test data derived from TCP herds with long testing histories. Age-distribution data from production-tested herds enabled estimation of reactor rates in animals that were culled or died. RESULTS: ELISA sensitivities at the first test round in herds achieving five, six and seven annual herd tests were 16.1, 14.9 and 13.5% respectively. The ELISA sensitivity in 2, 3 and 4-year-old animals at the first test round in herds testing seven times was 1.2, 8.9 and 11.6% respectively but remained between 20 and 30% in older age-groups. CONCLUSION: The sensitivity of the ELISA is considerably lower than previous estimates, probably because previous estimates were predominantly measured against faecal culture, which has subsequently been shown to have low sensitivity itself, and did not appreciate the long period that appears to precede detectable faecal excretion in most animals.     

Compliance of Victorian dairy farmers with current calf rearing recommendations for control of Johne's disease

Questionnaires were posted to 800 randomly selected registered Victorian dairy farmers in 1996. Five hundred and thirty-four responses were received and analysed. Johne's disease (JD) had been diagnosed on the farm of 13.2% of respondents in the last 5 years. JD was rated second only to neonatal diarrhoea in importance as a disease of calves, even though other diseases occurred more frequently. However, there was a low level of compliance with JD control recommendations by the respondents. There was no significant difference in the number of JD control recommendations adopted by farmers between the three major Victorian regions. There was a significant difference in compliance between farms having had a diagnosed case of JD and those that had not. Although there is awareness among dairy farmers of the importance of JD, there appears to be a poor implementation of measures by farmers to prevent the spread of the disease. Current JD control recommendations and the method of information transfer to Victorian dairy farms should be reassessed to ensure that dairy heifers are reared with minimal risk of transmission of JD.     

Control of Johne's disease in four commercial dairy herds in Iowa

A 6-year study was conducted in 4 dairy herds in Iowa in which Johne's disease was diagnosed previously. Fecal specimens were collected at 6-month intervals from animals 2 years of age and over for mycobacteriologic examination. Serum samples were obtained at 3-month intervals and tested by enzyme-linked immunosorbent assay (ELISA). The antigen used in the ELISA was a potassium chloride extract of a field strain of Mycobacterium paratuberculosis. The ELISA reactions were observed in 87% of the cows from which M. paratuberculosis was isolated. Dairy producers that participated in the Johne's control program reported reduced economic losses. Increased income was attributed to improved milk production, increased value of vaccinated animals sold as replacements to other dairy herds in which Johne's disease had been diagnosed, and the increased market value of slaughter animals removed from the herd.     

Financial effect of bovine Johne's disease in beef cattle herds in Australia

Objective To assess the financial effect of programs for controlling bovine Johne's disease (BJD) in beef herds. Design A spreadsheet simulation model of a self‐replacing beef herd in south‐eastern Australia selling 400‐kg steers at 15 months old. Methods The model calculated the monthly cash flow, and net present value (NPV) of cumulative cash flow, over 10 years. Four main control options were compared: (1) a base herd (no action to control the disease), (2) test and cull, and (3) partial and (4) total destocking. It was assumed that BJD was eradicated after 3 and 5 years with total and partial destocking, respectively, and not eradicated with a test and cull program. Scenarios were compared for both commercial and stud enterprises. Results If there was no discount on the sale price of cattle in commercial herds, deaths from BJD had to exceed 5% before the NPV of partial or total destocking was similar to taking no action to control the disease over a 10‐year period. When cattle sales incurred a 10% discount, deaths had to exceed 1% before the destocking strategies would break even after 10 years. Conclusion Control options for BJD should be carefully planned on an individual herd basis, as significant production and financial risks accompany destocking programs. Eradication will only be more profitable in the longer term, compared with living with the disease, when discounts on the sale of stock from infected herds are high. This can occur with the selling of store cattle or breeders. In stud herds, BJD will usually cause the total failure of the business.     

Decrease of Johne's disease prevalence and incidence in six Minnesota, USA, dairy cattle herds on a long-term management program

The objective of this prospective longitudinal field study was to describe changes in prevalence of seroconversion and fecal shedding and changes in incidence rate of seroconversion, fecal shedding and culling of milk cows for clinical signs of Johne's disease (JD) in six Minnesota (USA) herds participating to the JD Demonstration Herd Project (JDDHP) from 2000 to December 2005. Changes in prevalence and incidence rate were evaluated in light of the owner's compliance to the JDDHP using a risk assessment (RA) score. Adult cows were tested regularly using serum ELISA and bacterial fecal culture to evaluate progress made throughout the control program. Logistic regression was used to evaluate the association between the risk for a cow to test positive and the year on the program. After 5 years of follow-up, the proportion of cows that tested positive to serum ELISA and fecal culture (all positive cultures as well as moderate to heavy shedders only) decreased significantly from the first to the last year (8-3.1%, 10.4-5.6% and 3.1-1.5%, respectively). Cox proportional hazards regression was used to evaluate change of incidence rate across birth cohorts. Birth cohorts were defined by birth date of the animals with the reference cohort or oldest cohort being already 12-24 months of age at the onset of the long-term management program. All cohorts were censored at 45 months of age. Compared to cows from the reference cohort, cows from cohorts that could have benefitted from the JDDHP in their young age (less than 12 months of age at the start of the program or born later) were significantly less at risk of seroconversion and fecal shedding (hazard ratios for seroconversion, any fecal shedding and heavy shedding less than 0.63, 0.67 and 0.62, respectively). For the three herds achieving good management changes with a risk assessment score under 30 at their last year of the study, the cohorts that were born after the program was instituted did better than those born before the start of the program, implying that the program could have helped around birth as well for those herds. This study suggests that reduction of environmental contamination of heifers up to a year of age may have had some impact on the success of the program. The JDDHP appears more beneficial for herds achieving a better reduction of their RA score with a decrease risk for infection in very young calves.     

Infection rates in reactors to an absorbed ELISA used in a test and cull program for bovine Johne's disease

OBJECTIVE: To determine the proportion of cattle, whose sera gave positive reactions in a commercial enzyme linked immunosorbent assay (ELISA) for bovine Johne's disease, that were confirmed infected with Mycobacterium avium subsp paratuberculosis by histology and culture of tissues. PROCEDURE: Dairy cattle (n = 493) from the Echuca district of Victoria, whose sera were positive in the ELISA, were slaughtered at an abattoir where standard specimens were collected for histology and culture. Only if samples were histologically negative were further samples submitted for culture. RESULTS: The proportion of cattle in which infection was confirmed increased from 70.4% in 1996 to 89.4% in 2001 giving an overall confirmation rate of 79.9%. This was mainly because more reactors were confirmed by culture each year, the proportion increasing from 0% in 1997 to 27.5% in 2000 but decreasing to 16.7% in 2001. If all unconfirmed reactors were presumed to be uninfected, the minimum specificity of the ELISA was 99.62%. There were no significant differences between the age groups in the proportion confirmed infected. CONCLUSION: Confirmation rates and specificity of the ELISA were high when used in a typical JD-infected Victorian dairy cattle population. Imperfect sensitivity of histology and culture and the selection of reactors which favoured more false positives, means the estimates were probably conservative. Confirmation rates were not affected by age of ELISA reactor.     

A simulated surveillance program for bovine paratuberculosis in dairy herds in Norway

Monte Carlo simulation models were used to evaluate the feasibility and potential results of a proposed national survey of the prevalence of bovine paratuberculosis (PTB) in dairy herds in Norway. The expected herd prevalence was assumed to be 0.2% in the simulations. The low sensitivity of the ELISA test, the assumed low herd prevalence, the typical low within-herd prevalence of PTB and the small herd sizes all present problems in detection of the disease. Simulations with 500, 1000, 2500 and 6000 herds tested were done. Our results suggest that a national survey would not be feasible at present, due to the low probability of detecting infected herds and because of the high number of false-positive reactions that would be expected to occur.     

Prevalence and control of bovine cryptosporidiosis in German dairy herds

In a 5-year survey regarding its prevalence and importance in five German state veterinary laboratories Cryptosporidium was diagnosed annually in 19-36% of faecal samples either submitted to the laboratories or taken post mortem. In approximately half of the cases no other enteropathogens were detected. However, only 73% of 30 laboratories participating in a questionnaire survey routinely tested for this parasite, and the majority of researchers considered cryptosporidiosis to be of minor importance. In a placebo-controlled field study 152 suckling calves were treated daily against cryptosporidiosis either with sulfadimidine or with halofuginone (Halocur, Intervet) over 1 week. Treatment by oral drench started at the onset of diarrhoea in the herd. Oocyst excretion, faecal consistency and health status were recorded five times for a 3-week period. Oocyst excretion peaked 7-14 days in the placebo group after the onset of diarrhoea, and during that period prevalence and intensity of excretion were significantly lower in the halofuginone-treated group compared to the sulfadimidine and the placebo control groups. The health status (diarrhoea, dehydration) declined in all groups but was significantly (P<0.05-0.001) better in the halofuginone group in the first 2 weeks. Halofuginone effectively (P<0.05-0.001) reduced oocyst excretion and improved the health status of the treated animals, while sulfadimidine had no effect against Cryptosporidium.     

Progress in national control and assurance programs for bovine Johne's disease in Australia

Cattle strains of Mycobacterium paratuberculosis are known to infect cattle, goats and alpaca in southeastern Australia, where there are also significant numbers of farmed deer. Although sheep strains have recently been identified in some cattle in Australia, epidemiological evidence to date supports the distinction (between bovine Johne's disease (JD), caused by cattle strains in cattle, goats and alpaca, and ovine JD, caused by sheep strains in sheep and goats) for the purposes of control and assurance programs. The National Johne's Disease Control Program is coordinated by the Australian Animal Health Council, working with the livestock industries and with the Commonwealth, state and territory governments. The council also brokers industry and government funding for the program. The National Johne's Disease Market Assurance Program for Cattle was launched in 1996 as the first of a suite of voluntary national market assurance programs (MAPs) to assess and certify herds as negative for JD. By December 1998, over 550 herds had achieved an assessed negative status. A MAP was also launched for alpaca in 1998 and a program for goats should be finalized in early 1999. National standards for state control of JD through zoning, movement controls and procedures in infected and suspect herds have also been developed. The paper covers factors affecting development and implementation, uptake of and improvements to national control and assurance programs for bovine JD in Australia.     

Effect of compliance with recommended calf-rearing practices on control of bovine Johne's disease

OBJECTIVE: To assess the degree of compliance with recommended management procedures for the control of bovine Johne's disease and study the relationship between aspects of calf management and testing/disease outcomes in the herds. PROCEDURE: Fifty-four south Gippsland dairy herds participating in the Victorian bovine Johne's disease test and control program were visited between July and November 2002 and an audit of calf rearing practices was conducted. The results of testing completed under the program were analysed for each of the herds. Twenty seven management factors were examined for a relationship with the presence of clinical cases of Johne's disease or cattle with positive ELISA test results that were born after the completion of the second whole herd test. Logistic regression was used to examine the strength of relationships between the management practices and the frequency with which new cases of Johne's disease arose. RESULTS AND CONCULSIONS: Calves were removed from their dams within 12 hours of birth in only 17 (31.5%) of the herds. However, in all but one herd the calves were removed within 24 hours of birth. In 42 herds (77.8%) calf rearing facilities were adequately separated from adult cattle and the faeces from adult cattle. In 41 herds (75.9%) calves up to the age of 12 months were grazed on paddocks that were free of manure or effluent from adult cattle. However, in only 10 (18.5%) of the herds were all three of these calf management practices applied. Feeding whole milk containing antibiotic residues, or providing water for calves from birth, were found to have statistically significant associations with an increased occurrence of cases of bovine Johne's disease in the study herds. The practice of allowing cows to calve in a paddock was found to be associated with reduced occurrence of bovine Johne's disease. These associations were still found after analysis that included herd size, the number of clinical cases that had occurred in the herds before the start of testing, the number of animals with positive ELISA tests that were detected at the first test and the number of years of participation in the test and cull program. Early separation of newborn calves from cows and grazing calves under 12 months of age in areas free of adult cattle were not found to be protective against Johne's disease.     

Comparative sensitivity of various faecal culture methods and ELISA in dairy cattle herds with endemic Johne's disease

In three New South Wales dairy cattle herds with endemic Johne's disease, prevalence rates by faecal culture were determined to be 12, 18 and 22%, respectively. Whole herd faecal culture was shown to detect markedly more infected cattle than whole herd testing by the EMAI absorbed ELISA, particularly in the two herds with greatest prevalence. In the three study herds, five methods for whole herd faecal culture were compared in each. These included two methods based on primary culture on Herrold's egg yolk medium with mycobactin J (HEYM): (1) conventional decontamination with sedimentation and primary culture on HEYM; (2) Whitlock decontamination and culture on HEYM. The remaining three methods were based on radiometric (BACTEC) culture: (3) decontamination and filtration to BACTEC medium; (4) modified Whitlock decontamination to BACTEC medium and (5) Whitlock decontamination to BACTEC medium. For BACTEC cultures, two methods were compared as confirmatory tests for Mycobacterium paratuberculosis: mycobactin dependence on conventional subculture to HEYM and IS900 PCR analysis of radiometric media.Among 179 cattle tested simultaneously by all five culture methods, 38 cattle were confirmed to be shedding M. paratuberculosis. In identifying shedder cattle, method 5 was the most sensitive, followed by methods 2, 4, 1, and 3 was the least sensitive. The number of BACTEC cultures confirmed by mycobactin dependence or PCR was similar.     

Disposal and disease rates in British dairy herds between April 1998 and March 2002

Data derived over four years from 434 dairy herds in 1998/99 to 244 in 2001/02 revealed average disposal rates of 22.6 per cent per year, half of which were for poor fertility, mastitis and lameness. The quartile of herds with the lowest disposal rates sold an average of 11.5 per cent annually and the quartile with the highest rates sold 35.5 per cent. Average annual disease rates over the four years were as follows: for assisted calving 7.8 per cent, for digestive disease 1.2 per cent, for ketosis 0.5 per cent, for hypomagnesaemia 0.5 per cent, for hypocalcaemia 5.0 per cent and for injuries 0.8 per cent. The incidence of mastitis increased from 36.0 to 43.3 per cent of cows per year. The incidence of lameness decreased from 23.3 per cent in 1998/99 to 20.7 per cent in 2000/01 but increased to 21.9 per cent in 2001/02. Data received from the same 219 farms during the first three years showed no effective differences from the full set of data for each of the three years. The lowest annual incidences of mastitis and lameness on individual farms were below 7 per cent and 2.5 per cent, respectively. In general, housing cows in cubicles was associated with a greater risk of lameness, and housing them in straw yards with a greater risk of mastitis. However, some of the lowest rates of lameness were recorded in cubicle-housed cows and some of the lowest rates of mastitis were recorded in cows housed in yards. Larger herds were not associated, in general, with higher rates of mastitis.     

Efficiency of a herd health program in Swiss dairy herds

A retrospective analysis of the reproductive parameters was conducted in 15 dairy farms using a herd health monitoring system between 1995 and 1998. Five of these farms have used this monitoring process for many years (group 1) while 10 of them only initiated the process in 1996 (group 2). It was the aim of this study to evaluate the economic gain of the farms in each group due to the herd health monitoring program throughout the three year study period, by using Value Based Management (VBM), a model from the economic sciences. The mean calving to conception interval decreased from 93.3 to 84.0 days and from 104.9 to 86.7 days throughout the study period in groups 1 (P>0.05) and 2 (P < 0.05), respectively. The mean percentage of cows with calving to conception intervals below 115 days varied between 68.2% and 82.0% in group 1, while there was an increase form 65.2% to 78.6% in group 2 (P<0.05). There were no apparent trends in the reproductive culling rate throughout the study period (P>0.05), and the majority fell below 10%. Likewise, the first service conception rate varied between 52.7% and 56.6% and between 41.2% and 50.0%, in group 1 and 2, respectively. The number of services per conception varied between 1.6 and 1.8 and between 1.8 and 1.9, in groups 1 and 2, respectively. The number of days between calving and first service varied between 62.7 and 64.8 days in group 1, while it decreased significantly from 69.2 to 59.2 in group 2 (P<0.05). The time between first service and conception decreased from 30.6 to 22.0 days, and from 35.7 to 28.0 days in groups 1 and 2, respectively (P<0.05). Although there was an apparent increase of the detection rate of oestrus from 57.8% to 68.2% throughout the study period in group 1, it was not significant (P > 0.05). In group 2, however, the oestrus detection rate increased significantly from 53.0% to 69.9% (P < 0.05). The percent of detected oestrus within 42 days post partum increased from 33.1% to 38.1%, and from 24.1% to 40.9% in groups 1 and 2, respectively (P < 0.05). By 1998, four out of five farms in group 1, and five out of the eight farms where information was avail- year study period of CHF 25.- to CHF 609.- per cow and year. The calving to conception interval and the reproductive culling rate were the two most important parameters to determine the reproductive performance of the herd and the economic benefit of the herd health monitoring program. These findings support the implementation of a herd health monitoring program.     

Development of the Dutch Johne's disease control program supported by a simulation model

The development of a simulation model, "JohneSSim", was part of a research program aimed at designing a national Johne's disease control program for The Netherlands. Initially, the focus was mainly directed towards different compulsory "test-and-cull" strategies. However, the results from the JohneSSim model showed that eradication of Johne's disease based on such strategies would not be possible within 20 years and that it was also economically unattractive. However, improved calf management seemed to be more effective in reducing the prevalence within the same time period. Simulation of a strategy using an "ideal test" (80% sensitivity in all infected animals) showed a considerably faster decrease in prevalence. However, this strategy proved to be economically unattractive because of the high culling rate of (young) test-positive animals. The simulation model was also adapted to study beef cow herds. However, the results indicated that none of the strategies were able to reduce the mean true prevalence to almost zero for such herds. Only strategies based on "separation of calves and adult animals" proved to significantly reduce the prevalence but such a strategy is unpractical and uneconomic for Dutch beef cow herds. Due to this finding and the relative low number of Dutch beef cow farms, first priority has been given to the development of a Johne's disease control program for dairy farms. Based on the results of the "JohneSSim" model, the new national voluntary Johne's disease control program for dairy, Paratuberculosis Program Netherlands (PPN), started in September 2000. The PPN is based on a stepwise improvement of calf hygiene, with little dependency on "test and culling". The model results indicated that, if dairy farmers consistently carried out the necessary management adaptations, PPN considerably decreased prevalence and that it was economically more attractive than any previous plans.