Bulk Tank Milk Testing Research Articles

Serological testing of an equal-volume milk sample – a new method to estimate the seroprevalence of small ruminant lentivirus infection?

BackgroundIn cattle attempts to evaluate within-herd prevalence of various infectious and parasitic diseases by bulk-tank milk (BTM) testing with ELISA have been made with moderate success. The fact that BTM is composed of variable and unknown volumes of milk from individual lactating animals weakens the relationship between numerical result of the ELISA and the within-herd prevalence. We carried out a laboratory experimental study to evaluate if a pooled milk sample created by mixing an equal volume of individual milk samples from seropositive and seronegative goats, henceforth referred to as an equal-volume milk sample (EVMS), would allow for accurate estimation of within-herd seroprevalence of caprine arthritis-encephalitis (CAE) using 3 different commercial ELISAs. By mixing randomly selected milk samples from seronegative and seropositive goats, 193 EVMS were created – 93 made of seronegative samples and 100 with the proportion of seropositive individual milk samples (EVMS%POS) ranging from 1 to 100%. EVMS%POS could be considered as a proxy for the within-herd seroprevalence. Then, OD of EVMS (ODEVMS) of the 193 EVMS was measured using 3 commercial ELISAs for CAE – 2 indirect and 1 competitive.ResultsThe cut-off values of ODEVMS indicating SRLV infection were determined. The regression functions were developed to link ODEVMS with EVMS%POS. A significant monotonic relationship between ODEVMS measured with 2 commercial indirect ELISAs and EVMS%POS was identified. Two regression models developed on this basis described approximately 90% of variability and allowed to estimate EVMS%POS, when it was below 50%. High ODEVMS indicated EVMS%POS of > 50%.ConclusionOur study introduces the concept of serological testing of EVMS as a method of detecting SRLV-infected herds and estimating the proportion of strongly seropositive goats. Further field studies are warranted to assess practical benefits of EVMS serological testing.

Management practices associated with Johne's bulk tank milk ELISA positivity

Johne's disease (JD) control is often based on the culling of positive animals and the adoption of management practices that minimize exposure of young stock to the pathogen (Mycobacterium avium ssp. paratuberculosis). Throughout 2010 to 2013, the province of Ontario, Canada, instituted a voluntary Johne's control program consisting of whole-herd testing and risk assessment. The JD risk assessment evaluated 5 management areas to characterize herd JD risk. Using a modified milk ELISA technique with an optical density cut-off of 0.089, province-wide bulk tank milk (BTM) testing was used to assess the prevalence of JD high-risk herds at the end of the control program and again 4 yr after its completion. Approximately 71% of Ontario bulk tanks were classified as positive in 2017 compared with roughly 46% in 2013. In 2019, the same JD risk assessment used in the original program was readministered on 180 Ontario dairy farms. Using this cross-sectional approach, logistic regression models were built using data from the original program risk assessment and follow-up risk assessment as well as the BTM ELISA results to determine management factors associated with the control of JD. We demonstrated that management of the maternity area is an important factor in the control of Johne's disease. Although it is believed that the highest risk group for JD infection is calves under 6 mo, the cleanliness scores of older heifers and their exposure to mature cow manure was significantly associated with JD control; farms with highly contaminated weaned and bred heifers and those that had exposure to mature cow manure were more likely to be unsuccessful in their JD control efforts. Careful management of young calves appears to be important for JD control, and this management should continue even after calves have left the maternity area.

Economic analysis of biosecurity adoption in dairy farming: evidence from Ireland.

Given the significant negative impact of livestock disease outbreaks on animal and public health, preventing disease spread through biosecurity practices is important. In this study, we used a nationally representative dataset that included information on biosecurity practices of almost 300 Irish dairy farmers. We applied parametric and nonparametric estimation methods to assess the economic implications of adopting the following biosecurity measures: vaccination, bulk tank milk testing for diseases, and not pooling colostrum. We found mixed evidence of biosecurity practices on economic outcomes, measured as gross margins per cow. Specifically, we found that vaccination and testing bulk tank milk for diseases were significantly associated with better economic outcomes for dairy farms. However, we found no significant association with the economic performance of not pooling colostrum from more than one animal. Our findings have important policy implications required for targeting support for the adoption of biosecurity practices in dairy herds.

Evaluation of the MilA ELISA for the diagnosis of herd infection with Mycoplasma bovis using bulk tank milk and estimation of the prevalence of M. bovis in Australia

Infection with Mycoplasma bovis has been identified as a growing threat in dairy industries worldwide and there is an urgent need for an inexpensive and accurate herd-level screening tool to identify herds that have been exposed to M. bovis. This study aimed to evaluate the use of the MilA ELISA for testing bulk tank milk (BTM) samples for antibodies against M. bovis and estimate a suitable cut-off and diagnostic sensitivity (DSe) and specificity (DSp) for this assay. An optimal cut-off was then applied for investigating the geographical and seasonal distribution of infection with M. bovis in Australia. A total of 5554 BTM samples from 2683 dairy herds were collected during March, August and December 2017. BTM samples were tested in the MilA ELISA and a cut-off of 29 antibody units (AU) was estimated to be optimal using Bayesian latent class analysis which makes no assumption about the true disease status of herds under investigation. At this cut-off, the DSe and DSp were estimated to be 96.6% (95% highest probability density [HPD] interval: 87.0, 99.8) and 94.2% (95% HPD: 89.9, 97.4), respectively. The diagnostic specifications were found to vary markedly with stage of the production cycle, suggesting that targeted sampling was needed to maximize accuracy. We also found distinct differences in the apparent prevalence of M. bovis in different dairying regions, as well as seasonal variation. The highest apparent prevalence of M. bovis was observed in samples collected in March and an overall drop in the proportion of positive herds was seen from March to December. Overall, this study provides insights into the dynamics of BTM antibodies against M. bovis in Australian dairy herds and how the MilA ELISA can be applied for bulk tank milk testing.

Use of scenario tree modelling to plan freedom from infection surveillance: Mycoplasma bovis in New Zealand

Since mid-2018, the New Zealand (NZ) Ministry for Primary Industries (MPI) has been operating an eradication program for an incursion of Mycoplasma bovis. Although NZ is still delimiting the outbreak, consideration is being given to how freedom from M. bovis will be demonstrated. Rapid demonstration of freedom will minimise the length of the program, significantly reducing its financial burden. This collaborative research was undertaken to help inform planning of surveillance to demonstrate freedom after M. bovis is believed eradicated.Scenario tree modelling (STM) involves assimilating multiple surveillance system components to determine whether disease is absent. STM has infrequently been used to plan appropriate surveillance but this was the approach used here. A stochastic simulation model was implemented in R. The model represented the NZ commercial dairy and non-dairy cattle industries and the current surveillance components that are also planned to be used to gather evidence of absence of M. bovis once it is eradicated. Different surveillance intensities and risk based versus random surveillance were simulated and compared for probability of freedom, financial cost of sampling and testing and the time to demonstrate freedom.The results indicate that the current surveillance components will enable demonstration of freedom. Surveillance components included bulk tank milk testing, herd testing and testing at meat processing plants, predominantly using an imperfect ELISA. Several combinations of surveillance components appeared most efficient achieving >95 % confidence of freedom over 2–4 years, whilst sampling 4–7 % of the non-dairy herds and less than 25 % of dairy herds annually. The results indicate that surveillance intensity can be lower than is currently occurring to support the delimiting phase, thereby saving significant resources in the post eradication phase (proof of freedom phases).Further consideration is required to enable the assumption of 100 % herd specificity made in the model to be achieved. The ELISA used is very specific, but will yield some false positives that must be resolved to their true status. This may occur for example through modified diagnostic test interpretation (e.g. cut point optimisation at individual and herd level) or resolution of putative false positive herds with epidemiological investigation.In conclusion this research demonstrates the utility of STM for planning surveillance programs, and in this instance has highlighted efficient and effective surveillance components for demonstrating freedom from M. bovis in NZ. It also highlights the need to achieve 100 % specificity for M. bovis in herds tested during the proof of freedom phases.

Evaluation of risk-based surveillance strategies for Salmonella Dublin in Danish dairy herds by modelling temporal test performance and herd status classification errors

The potential risk-based improvement of the Salmonella Dublin surveillance programme in Danish dairy herds was investigated, considering herd status misclassifications due to testing errors. The programme started in October 2002. Currently (early 2021) all dairy herds are classified based on quarterly bulk tank milk (BTM) testing with an indirect antibody ELISA (iELISA). Over the last two decades, the prevalence of herds classified as “likely infected” (levels 2,3) reduced remarkably. However, since 2015, the apparent prevalence has increased again, calling for improved surveillance and control to protect animal and human health. A deterministic simulation model based on data (2018–2019) from 2283 dairy herds in level 1 (“most likely free from infection”), was developed to estimate status misclassifications as false negative (FN) and false positive (FP) herds, under two testing strategies. These were: (A) the current system based on quarterly BTM testing only, and (B) an alternative strategy based on additional blood testing of up to eight calves, within herds at high risk of infection (HR). Both strategies were evaluated using three risk classification methods (I to III) and four sensitivity analysis scenarios (SA1-4), where different temporal performances were simulated for the iELISA in BTM. To apply strategy B, the best high-risk classification method (II), which combined managerial applicability and minimized errors, would require testing approximately 1000 calves across 127 HR herds. In that case, strategy A would cause 3 FNs and 67 FPs, by assuming annual BTM sensitivity (BTMSe) 95% conditional on a 1-year disease history and specificity (BTMSp) 97%. Whereas strategy B could cause a similar number of FNs, but 7 FPs more, assuming a sensitivity (Se) of 77% and specificity (Sp) of 99% in individual blood-samples (SA1). Assuming also quarterly BTMSe 53% and BTMSp 99.9% (SA4), strategy A derived 28 FNs and 2 FPs, while strategy B resulted in 6 FNs less and 8 FPs more. Therefore, strategy B could improve early detection of infected HR herds, while strategy A would avoid more unnecessary restrictions in false-positive herds. This improves knowledge on the potential use of additional blood testing in HR herds and illustrates how deterministic modelling can be used to improve disease surveillance and control.

Serological screening for Coxiella burnetii in the context of early pregnancy loss in dairy cows.

Q fever is one of the commonest infectious diseases worldwide. A Coxiella burnetii prevalence of 97.6% has been found by ELISA and PCR tests of the bulk tank milk in dairy cattle farms of Hungary. The herd- and individual-level seroprevalence rates of C. burnetii in the examined dairy cows and farms have dramatically increased over the past ten years. Three high-producing industrial dairy farms were studied which had previously been found ELISA and PCR positive for C. burnetii by bulk tank milk testing. Coxiella burnetii was detected in 52% of the 321 cows tested by ELISA. Pregnancy loss was detected in 18% of the cows between days 29-35 and days 60-70 of gestation. The study found a higher seropositivity rate (80.5%) in the cows that had lost their pregnancy and a seropositivity of 94.4% in the first-bred cows that had lost their pregnancy at an early stage. The ELISA-positive pregnant and aborted cows were further investigated by the complement fixation test (CFT). In dairy herds an average of 66.6% individual seropositivity was detected by the CFT (Phase II) in previously ELISA-positive animals that had lost their pregnancy and 64.5% in the pregnant animals. A higher (Phase I) seropositivity rate (50.0%) was found in the cows with pregnancy loss than in the pregnant animals (38.5%). The high prevalence of C. burnetii in dairy farms is a major risk factor related to pregnancy loss.

Evaluation of the English bovine brucellosis surveillance system considering probability of disease introduction and non-random sampling

The English surveillance system for bovine brucellosis was evaluated. The confidence in detecting at least one infected herd in the local population (surveillance system sensitivity or SSe), and the confidence in freedom from disease (PFree) adjusted (PFreeAdj) for the probability of disease introduction from abroad by imported animals (PIntro), were estimated for quarterly surveillance periods of 2016; because dairy herds were tested quarterly on bulk tank milk (BTM) with an antibody indirect ELISA. A stochastic model was developed and six surveillance components (representing also the local population strata), were evaluated. All English herds and their relative risk (RRs) of infection within each stratum were considered. The importance of each component was assessed using actual national data, which reflected non-random sampling. The contribution of the abortions testing was assessed with particular focus, because a decline in statutory submissions was observed in recent years. Beef herds without submissions (B-NoTest herds) at the laboratories were still considered as a population stratum, where infected cattle could be imported. Additionally, we evaluated the importance of different hypothetical design between-herds prevalence (Ph) values, at which the country could be classified as “infected”. The potential negative effect on SSe due to the dilution of antibodies when individual samples are pooled within BTM and tested by the milk iELISA, was also investigated. The quarterly median SSe and PFreeAdj were both ≥ 95 % if at least four (0.008 %) herds were infected in the country due to independent import events. The system appeared able to substantiate Official Brucellosis Free (OBF) status frequently (on quarterly basis) using Ph=0.2 % (EU legislation). The component based only on BTM testing (M herds) showed the highest sensitivity; while the surveillance components based on abortions or post import calving (PIC) testing, had very low sensitivity at the (considered) Ph values lower than 0.2 %. In contrast, at Ph = 0.2 %, components based on abortion testing had median sensitivity between 91.3 % and 99.9 %, and the dilution effect on BTM testing did not change remarkably the SSe and PFreeAdj. When Ph was set to 1–2 infected herds (0.002–0.004 %), these were usually allocated by the model within the B-NoTest stratum (the largest stratum) and SSe reduced. Thus, if policy considers necessary increasing the SSe for low Phs (system’s optimization as an early warning system); the cost efficiency of active risk based surveillance in beef herds (considering imports) could be investigated in the future.

Evaluation of national surveillance methods for detection of Irish dairy herds infected with Mycobacterium avium ssp. paratuberculosis

The aim of this study was to evaluate the utility and cost-effectiveness of a range of national surveillance methods for paratuberculosis in Irish dairy herds. We simulated alternative surveillance strategies applied to dairy cattle herds for the detection of Mycobacterium avium ssp. paratuberculosis (MAP)-infected herds (case-detection) or for estimation of confidence of herd freedom from infection (assurance testing). Strategies simulated included whole-herd milk or serum serology, serology on cull cows at slaughter, bulk milk tank serology, environmental testing, and pooled fecal testing. None of the strategies evaluated were ideal for widespread national case-detection surveillance. Herd testing with milk or serum ELISA or pooled fecal testing were the most effective methods currently available for detection of MAP-infected herds, with median herd sensitivity >60% and 100% herd specificity, although they are relatively expensive for widespread use. Environmental sampling shows promise as an alternative, with median herd sensitivity of 69%, but is also expensive unless samples can be pooled and requires further validation under Irish conditions. Bulk tank milk testing is the lowest cost option and may be useful for detecting high-prevalence herds but had median herd sensitivity <10% and positive predictive value of 85%. Cull cow sampling strategies were also lower cost but had median herd sensitivity <40% and herd positive predictive values of <50%, resulting in an increased number of test-positive herds, each of which requires follow-up herd testing to clarify status. Possible false-positive herd testing results associated with prior tuberculosis testing also presented logistical issues for both cull cow and bulk milk testing. Whole-herd milk or serum ELISA testing are currently the preferred testing strategies to estimate confidence of herd freedom from MAP in dairy herds due to the good technical performance and moderate cost of these strategies for individual herd testing. Cull cow serology and bulk tank milk sampling provide only minimal assurance value, with confidence of herd freedom increasing only minimally above the prior estimate. Different testing strategies should be considered when deciding on cost-effective approaches for case-detection compared with those used for building confidence of herd freedom (assurance testing) as part of a national program.

Assessment of the cost effectiveness of compulsory testing of introduced animals and bulk tank milk testing for bovine viral diarrhea in Japan.

Bovine viral diarrhea (BVD) is a chronic disease of cattle caused by infection with BVD virus (BVDV) and can result in economic losses within the livestock industry. In Japan, the test and culling policy is a basic control measure, and implementation of an adequate vaccination program is recommended as a national policy. In addition, optional control measures, including compulsory testing of introduced animals and bulk tank milk (BTM) testing as a mass screening method, are used in several provinces, but their efficacy has not been completely assessed. We evaluated these control measures using the scenario tree model of BVD in Japan, developed in the previous study. The model outputs indicated that compulsory testing of all introduced cattle, rather than only heifers and/or non-vaccinated cattle, was cost effective and reduced the risk of BVDV introduction due to animal movement and that BTM testing could effectively monitor most part of the cattle population. Vaccination coverage and BVDV prevalence among introduced cattle could also affect the cost effectiveness of compulsory testing of targeted cattle, particularly under low vaccination coverage or high BVDV prevalence. However, even with the implementation of a highly effective monitoring scheme for many years, BVD risk could not be eliminated; it instead converged at a very low level (0.02%). Disease models with a cost-effective output could be a powerful tool in developing a control scheme for chronic animal diseases, including BVD, with the consent of relevant stakeholders.

A novel pooled milk test strategy for the herd level diagnosis of Dictyocaulus viviparus

Current diagnostic methods for detecting the presence or absence of Dictyocaulus viviparus in dairy herds, are insensitive when based on detection of antibody levels in bulk tank milk (BTM). Here we present a novel technique to confirm the presence of the parasite based on a pooled-milk sample from 10 randomly selected first – lactation heifers (FLH). This study was run in two parts. First, a longitudinal study was performed to look at infection dynamics in milk samples across the grazing season using a prototype ELISA developed by Svanova (Boehringer-Ingelheim, Uppsala). We identified that mean ODR values in milk samples from FLH was significantly higher than that for older cows (0.13 versus 0.07 respectively, p < 0.001) suggesting that samples from the FLH cohort should be pooled to produce the test. Second, the pooled – milk test was evaluated on a cross-sectional survey of UK dairy herds (n = 25 grazing and n = 25 zero-grazing herds) to evaluate test performance under field conditions. The optical density ratio (ODR) cut-off value for our pooled-milk test using 10 FLH milk samples was optimal at a value of 0.16. Pooling 10 FLH samples created a sensitivity and specificity of 66.7% and 95.5% respectively. In comparison, whole-herd BTM samples had a maximum sensitivity of 37.5% and specificity of 63.6% at an ODR cut-off of 0.18. The area under the curve according to receiver-operative-characteristic (ROC) analysis was high for the 10-heifer test (0.87) but poor for the whole herd BTM testing (0.45). This study provides a more sensitive diagnostic test strategy for the screening of D.viviparus in dairy herds. Testing herds at the end of a grazing season would facilitate the planning of effective control measures, such as the use of the lungworm vaccination or strategic deworming, for the following grazing season. This may prove to be a useful test strategy for the diagnosis of a variety of parasitic diseases of livestock.

Herd level estimation of probability of disease freedom applied on the Norwegian control program for bovine respiratory syncytial virus and bovine coronavirus

A national control program against bovine respiratory syncytial virus (BRSV) and bovine coronavirus (BCV) was launched in Norway in 2016. A key strategy in the program is to test for presence of antibodies and protect test-negative herds from infection. Because these viruses are endemic, the rate of re-introduction can be high, and a disease-free status will become more uncertain as time from testing elapses. The aim of this study was to estimate the probability of freedom (PostPFree) from BRSV and BCV antibodies over time by use of bulk tank milk (BTM) antibody-testing, geographic information and animal movement data, and to validate the herd-level estimates against subsequent BTM testing.BTM samples were collected from 1148 study herds in West Norway in 2013 and 2016, and these were analyzed for BRSV and BCV antibodies. PostPFree was calculated for herds that were negative in 2013/2014, and updated periodically with new probabilities every three months. Input variables were test sensitivity, the probability of introduction through animal purchase and local transmission. Probability of introduction through animal purchase was calculated by using real animal movement data and herd prevalence in the region of the source herd. The PostPFree from the final three months in 2015 was compared to BTM test results from March 2016 using a Wilcoxon Rank Sum Test.The probability of freedom was generally high for test-negative herds immediately after testing, reflecting the high sensitivity of the tests. It did however, decrease with time since testing, and was greatly affected by purchase of livestock. When comparing the median PostPFree for the final three months to the test results in 2016, it was significantly lower (p < 0.01) for test positive herds. Furthermore, there was a large difference in the proportion of test positive herds between the first and fourth quartile of PostPFree. The results show that PostPFree provides a better estimate of herd-level BTM status for both BRSV and BCV than what can be achieved by relying solely on the previous test-result.

Use of a breeding bull and absence of a calving pen as risk factors for the presence of Mycoplasma bovis in dairy herds

Mycoplasma bovis is an important cause of pneumonia and mastitis in cattle throughout the world, often reported as emerging. In absence of an effective vaccine for M. bovis, current prevention and control strategies rely on the identification of risk factors for within- and between-herd spread. The objective of this study was to determine the prevalence of M. bovis in Belgian dairy herds and to identify risk factors associated with a positive PCR or antibody ELISA bulk tank milk (BTM) test. A cross-sectional study was performed in 2016 on 100 dairy farms, analyzing BTM using PCR and antibody ELISA. Information on herd-level risk factors focusing on biosecurity and management were collected through a questionnaire and sourced from the national herd identification system (SANITRACE, Animal Health Service Flanders). Multivariable logistic regression was used to identify herd-level risk factors for the presence of M. bovis DNA and antibodies in BTM. The apparent prevalence on BTM was 7 and 17% for PCR and antibody ELISA, respectively. The true prevalence was 7.1% [95% confidence interval (CI) = 2.1-11.5%] and 24.8% (95% CI = 16.4-33.2%). There was no overlap between ELISA- and PCR-positive farms, resulting in a combined true prevalence of 31.8% of the Belgian farms being in recent contact with M. bovis. Risk factor analysis showed that herds with a breeding bull [M. bovis-positive results for 45.5 and 13.6% of herds with and without a bull, respectively, odds ratio = 4.7 (95% CI = 1.1-19.8)] and without a calving pen [M. bovis-positive result in 52.4 and 20.6% of the herds without and with a calving pen, respectively, odds ratio = 3.7 (95% CI = 1.06-12.5)] had higher odds to harbor M. bovis antigen or antibodies in BTM. In conclusion, the present study points to a several fold increase in the prevalence of M. bovis in Belgian dairy herds. The importance of the breeding bull and calving pen in the between- and within-herd spread of M. bovis might have been underestimated in the past. Focusing on these factors might contribute to more effective control programs in the future.

Optimising cost-effectiveness of freedom from disease surveillance—Bluetongue Virus Serotype 8 as an example

The aim of this study was to propose a procedure for optimising the cost-effectiveness of vector borne disease surveillance using a scenario tree model and cost-effectiveness analysis. The surveillance systems for Bluetongue Virus serotype 8 (BTV-8) implemented in Switzerland and Belgium were used as examples. In twenty four different, simulated population structures, passive surveillance and five designs of active surveillance were investigated. The influence of surveillance system design and parameters such as farmer disease awareness, veterinary disease awareness, herd and within-herd design prevalence on the overall surveillance system sensitivity were assessed. Furthermore, the cost-effectiveness of mandatory and voluntary vaccination regimes in relation to disease surveillance was investigated.Under the assumption that BTV-8 manifests clinically, freedom from disease in a population can be established with almost certainty over the period of one year using clinical surveillance alone. Additional investment in active surveillance would therefore economically only be justified, if no clinical manifestation is suspected or other surveillance objectives are to be provided such as early detection. The best cost-effectiveness is obtained by sampling more herds rather than more animals within a herd. Mandatory vaccination reduces the cost of surveillance by 0.26 € per vaccine and voluntary vaccination only marginally reduces the cost of risk-based surveillance, by reducing the population at risk. Finally, in populations with predominantly dairy cattle, bulk-tank milk testing is the method of choice to actively demonstrate freedom from disease.

Short communication: Correlation between within-herd antibody-prevalence and bulk tank milk antibody levels to Mycobacterium avium ssp. paratuberculosis using 2 commercial immunoassays

The objective of this study was to determine the correlation between the results obtained with the ELISA technique for antibodies to Mycobacterium avium ssp. paratuberculosis in serum and bulk tank milk at the herd level. For this purpose, 203 samples of bulk tank milk were analyzed with 2 commercial ELISA from dairy herds with a prevalence of seropositive animals that was also determined. In regard to the reference test (results in blood serum), the sensitivity of the bulk tank milk test to detect high-positive herds (≥10% seroprevalence) ranged from 85.7 to 71.4%. The specificity to detect herds with no seropositive animals ranged from 70.5 to 53%. In a quantitative approach, Pearson correlation coefficients, reported as a measure of the linear association between herd seroprevalences and transformed optical density values recorded in bulk tank milk, were 0.39 and 0.54 for the studied ELISA. Although the test results were relatively fairly correlated with the within-herd prevalence, the practical utility of bulk tank milk testing for Mycobacterium avium ssp. paratuberculosis seems limited, especially regarding specificity.

Bovine herpesvirus 1: within-herd seroprevalence and antibody levels in bulk-tank milk.

The aim of the present study was to establish a relationship between the results obtained with the enzyme-linked immunosorbent assay (ELISA) technique for antibodies (against bovine herpesvirus 1) in serum and those in milk at the herd level. For this purpose, 275 samples of bulk-tank milk were analysed with glycoprotein E (gE) antibody ELISA and 207 more were analysed with glycoprotein B (gB) antibody ELISA (482 in total). All of these samples came from dairy herds whose seroprevalence was also evaluated. The results of this study were then used to analyse the sensitivity of the bulk-tankmilk test in detecting herds with a high risk of active infection (>60% seroprevalence) and its specificity in detecting those with few (<20%) or no seropositive animals. In regard to the reference test (results in blood serum), the sensitivity of the bulk-tankmilk test in detecting herds with >60% seropositive animals was 100% for both gE and gB ELISAs. The specificity figures, for gE and gB ELISAs, respectively, were 88.4% and 99.1% for infection-free herds and 72.6% and 96% for herds with <20% seroprevalence. In a quantitative approach, Pearson's correlation coefficients, reported as a measure of linear association between herd seroprevalences and transformed optical density values recorded in bulk-tank milk, were -0.63 for gE ELISA and 0.67 for gB ELISA.

Association between Dictyocaulus viviparus status and milk production parameters in Dutch dairy herds

The objective of this study was to estimate the association between Dictyocaulus viviparus bulk tank milk (BTM) test results and milk production and milk composition parameters in adult Dutch dairy cattle herds. Bulk tank milk samples were collected in August and November 2013, and ELISA tests were performed. Two hundred BTM positive (BTM+) and 200 BTM negative (BTM–) herds were selected based on their BTM test result of November 2013, obtained from a list of farms that participated in the Dutch GD Animal Health voluntary monitoring program for controlling nematode infections. The relationship between D. viviparus BTM status and 3 production parameters (milk production, milk fat %, and milk protein %) in summer (June to August 2013) and autumn (September and October 2013) was investigated using generalized linear mixed models. Production data were available for 126 BTM– herds and 109 BTM+ herds. Results showed that a positive D. viviparus status was associated with decreased milk production (June: –1.01, July: –1.19, August: –1.68, September and October: –1.33kg/cow per d). Milk fat percentage was 0.14% and 0.08% lower during summer and autumn, respectively, in BTM+ herds. No significant association was demonstrated between a positive BTM test result and milk protein percentage. Because a strong correlation was present between the BTM status for D. viviparus and that for Ostertagia ostertagi, these losses cannot be attributed to one of the two parasites. However, it is clear that these parasite infections have a considerable effect on production.

Caprine arthritis encephalitis and caseous lymphadenitis in goats: use of bulk tank milk ELISAs for herd-level surveillance

The objective of this study was to evaluate the diagnostic performance of two ELISA tests applied to bulk tank milk (BTM) as the first part of a two-step test scheme...

Prevalence and risk factors for Coxiella burnetii (Q fever) in Dutch dairy cattle herds based on bulk tank milk testing

Despite cattle herds can harbor Coxiella burnetii, risk factors for C. burnetii presence in dairy cattle herds are largely unknown. Therefore, C. burnetii herd prevalence and risk factors for bulk tank milk (BTM) positivity were investigated. In this cross-sectional study, a questionnaire was filled out by the farmer and BTM from 301 farms was tested by ELISA for presence of C. burnetii antibodies and PCR for presence of C. burnetii DNA. Risk factors were identified by univariable and multivariable logistic regression analyses. Antibodies to C. burnetii were detected in 81.6% (CI: 77.2–85.9) and C. burnetii DNA in 18.8% (CI: 14.4–23.1) of the BTM samples. Herd size (OR=1.1 per 10 cows), cleaning the bedding of the cubicles at most every other day (OR=2.8) and purchase of cattle from at least two addresses (OR=3.1) showed a significant and positive association with ELISA positivity and use of an automatic milking system a negative association (OR=0.3). Risk factors for PCR positivity were purchase of cattle from at least two delivery addresses (OR=3.2), presence of cows with ticks (OR=2.0), use of an automatic milking system (OR=0.2) and presence of goats or sheep on the farm (OR=0.4). Biosecurity and general hygiene seem associated with introduction and spread of C. burnetii in dairy herds.

Lungworm Infections in German Dairy Cattle Herds — Seroprevalence and GIS-Supported Risk Factor Analysis

In November 2008, a total of 19,910 bulk tank milk (BTM) samples were obtained from dairy farms from all over Germany, corresponding to about 20% of all German dairy herds, and analysed for antibodies against the bovine lungworm Dictyocaulus viviparus by use of the recombinant MSP-ELISA. A total number of 3,397 (17.1%; n = 19,910) BTM samples tested seropositive. The prevalences in individual German federal states varied between 0.0% and 31.2% positive herds. A geospatial map was drawn to show the distribution of seropositive and seronegative herds per postal code area. ELISA results were further analysed for associations with land-use and climate data. Bivariate statistical analysis was used to identify potential spatial risk factors for dictyocaulosis. Statistically significant positive associations were found between lungworm seropositive herds and the proportion of water bodies and grassed area per postal code area. Variables that showed a statistically significant association with a positive BTM test were included in a logistic regression model, which was further refined by controlled stepwise selection of variables. The low Pseudo R2 values (0.08 for the full model and 0.06 for the final model) and further evaluation of the model by ROC analysis indicate that additional, unrecorded factors (e.g. management factors) or random effects may substantially contribute to lungworm infections in dairy cows. Veterinarians should include lungworms in the differential diagnosis of respiratory disease in dairy cattle, particularly those at pasture. Monitoring of herds through BTM screening for antibodies can help farmers and veterinarians plan and implement appropriate control measures.