Herd-level Prevalence Research Articles

Prevalence of Mycobacterium avium subsp. paratuberculosis infection in dairy herds in Northern Antioquia (Colombia) and associated risk factors using environmental sampling

This cross-sectional study aimed to determine Mycobacterium avium subsp. paratuberculosis (MAP) herd-level prevalence using a quantitative real-time PCR method (qPCR), performed on environmental samples. Secondly, the study aimed to explore herd-level risk factors associated with the presence of MAP in dairy herds with in-paddock milking facilities of the Northern region of the Province of Antioquia (Colombia). Study herds (n = 292) located in 61 different districts from six municipalities were randomly selected amongst 7794 dairies registered in the foot-and-mouth disease vaccination records from 2015. The sampling strategy considered a proportional allocation, both at municipality and district level. Participant herds were visited once between June and October 2016 to collect one composite environmental sample and to complete a risk assessment questionnaire. Each composite environmental sample contained material from six different sites of concentration of adult cattle and/or high traffic areas (e.g. areas surrounding waterers and feeders, areas surrounding the current mobile milking-unit places). Identification of MAP was achieved using a duplex qPCR (Bactotype MAP PCR Kit®, Qiagen). A herd was considered as MAP infected if the environmental sample was positive in the qPCR. Information about the general characteristics of the herd, management practices, and knowledge about the disease was collected using the risk-assessment questionnaire. The information on risk factors was analyzed using a multivariable logistic regression model. The apparent herd-level prevalence was 4.1% (12/292; 95% CI: 1.8–6.4). Herds with a history of mixed farming of cattle with other ruminants had higher odds of being MAP infected than herds without (OR = 3.9; 95% CI: 1.2–13.2). Our study demonstrates the MAP prevalence in dairy herds from Antioquia, Colombia and the possible relationship between MAP environmental positivity with the history of mixed farming of cattle with other susceptible ruminants.

Establishing post-outbreak freedom from African horse sickness virus in South Africa's surveillance zone.

An African horse sickness (AHS) outbreak occurred in South Africa's AHS controlled area in autumn 2016. A freedom from disease survey was performed to establish the likelihood of ongoing circulation of the associated virus during the same period the following year. A single-stage surveillance strategy was employed with a population-level design prevalence of 1% to establish a survey population sensitivity of 95% (probability that one or more positive horses would be detected if AHS was present at a prevalence greater than or equal to the design prevalence). In March 2017, a total of 262 randomly selected horses from 51 herds were sampled from the 2016 outbreak containment zone. Three within-herd and herd-level design prevalence scenarios were used in evaluating the post-survey probability of freedom. Depending on the underlying design prevalence scenarios, effectively ranging between 0.8% and 6.4%, and the use of informed or uninformed priors, the probability of freedom derived from this surveillance ranged between 73.1% and 99.9% (uninformed prior) and between 96.6% and 100% (informed prior). Based on the results, the authors conclude that it is unlikely that the 2016 AHS virus was still circulating in the autumn of 2017 in the 2016 outbreak containment zone. The ability to perform freedom from disease surveys, and also to include risk-based methods, in the AHS controlled area of South Africa is influenced by the changing underlying population at risk and the high level of vaccination coverage in the horse population. Ongoing census post-outbreak must be undertaken to maintain a valid sampling frame for future surveillance activity. The seasonality of AHS, the restricted AHS vaccination period and the inability to easily differentiate infected from vaccinated animals by laboratory testing impact the ability to perform a freedom from disease survey for AHS in the 12months following an outbreak in the controlled area.

Effects of Age and Environment on Adaptive Immune Responses to Mycobacterium avium subsp. paratuberculosis (MAP) Vaccination in Dairy Goats in Relation to Paratuberculosis Control Strategies.

Paratuberculosis infection is caused by Mycobacterium avium subsp. paratuberculosis (MAP). In the Netherlands, 75% herd level prevalence of caprine paratuberculosis has been estimated, and vaccination is the principal control strategy applied. Most goat dairy farms with endemic paratuberculosis systematically vaccinate goat kids in the first months of life with a commercially available whole cell MAP vaccine. We hypothesized that the development of adaptive immune responses in goats vaccinated at young age depends on the environment they are raised in, and this has implications for the application of immune diagnostic tests in vaccinated dairy goats. We evaluated the early immune response to vaccination in young goat kids sourced from a MAP unsuspected non-vaccinated herd and raised in a MAP-free environment. Subsequently we compared these with responses observed in birth year and vaccination matched adult goats raised on farms with endemic paratuberculosis. Results indicated that initial adaptive immune responses to vaccination are limited in a MAP-free environment. In addition, adult antibody positive vaccinated goats raised in a MAP endemic environment are less likely to be IS900 PCR-positive as compared to antibody negative herd mates. We conclude that test-and-cull strategies in a vaccinated herd are currently not feasible using available immune diagnostic tests.

An investigation of dairy calf management practices, colostrum quality, failure of transfer of passive immunity, and occurrence of enteropathogens among Australian dairy farms

Calf preweaning morbidity and mortality risks have been reported as high in several countries, with average values approximating 35 and 7%, respectively. However, limited data are available for calf morbidity and mortality risks on Australian dairy farms. The aims of this study were (1) to investigate current calf management practices on dairy farms in Australia and their association with herd-level morbidity and mortality using a questionnaire-based, cross-sectional study; and (2) to estimate the prevalence of common enteropathogens causing diarrhea, the failure of passive transfer of immunity, and poor colostrum quality in a sample of Australian dairy farms. We analyzed 106 completed questionnaires and samples from 23 farms (202 fecal, 253 calf serum, and 221 colostrum samples). Morbidity and mortality risks reported by farmers in preweaned heifers were 23.8 and 5.6%, respectively. These risks were above the Australian dairy industry targets in 75.5 and 66.7% of respondents. The zoonotic pathogens Cryptosporidium spp. and Salmonella spp. were the most prevalent enteropathogens, with a true prevalence of 40.9 and 25.2%, respectively. Salmonella O-group D was present in 67.9% of Salmonella-positive samples, followed by O-groups B (17.9%) and C (10.7%). Failure of transfer of passive immunity (IgG <10 g/L) was observed in 41.9% of calves (mean herd-level prevalence of 36.2%), and only 19.5% of colostrum samples met the standards for immunoglobulin content and microbiological quality. Collectively, these data indicate that there is still considerable room for improvement in calf-rearing practices on Australian dairy farms, particularly with regard to colostrum management and feeding hygiene.

Bayesian estimation of herd-level prevalence and risk factors associated with BoHV-1 infection in cattle herds in the State of Paraíba, Brazil

A cross-sectional study was carried out to estimate the animal- and herd-level prevalence of bovine herpesvirus 1 (BoHV-1) infection in cattle in the State of Paraíba, and to identify risk factors associated with herd-level infection. The state was divided into three sampling strata, and for each stratum, the prevalence of herds infected with BoHV-1 was estimated through a two-stage sampling survey carried out from September 2012 to January 2013. In total, 2443 animals were sampled from 478 herds. A virus-neutralization test was used for BoHV-1 antibody detection. A Bayesian latent-class model was used to describe the data, taking into account imperfect diagnostic test characteristics and the non-independence of test results from animals within the same herd, and using a dynamic within-model risk factor selection method based on indicator variable selection. The adjusted herd-level prevalence was estimated to be 84% (95% CI: 80–88%) for the State of Paraíba, and the animal-level prevalence was estimated to be 73% (95% CI: 66–84%). Only five of the available risk factors were used by the model, with the three most influential being disposal of aborted foetuses (3.78, 95% CI: 1.11–13.85), sharing resources with other farms (3.0, 95% CI: 1.1–8,6), and a herd size of > 23 animals (2.5, 95% CI: 1.1–6.0). Our findings suggest that the animal- and herd-level seroprevalence of BoHV-1 infection in the State of Paraíba is high. While some risk factors such as herd size and sharing resources were identified as risk factors for BoHV-1 infection, these risk factors are initially likely to be of only minor relevance in a control programme due to the extremely high prevalence of infected farms. However, the results are relevant to the risk of reintroduction of disease on farms that have previously eradicated the disease.

Prevalence of excessive negative energy balance in commercial United Kingdom dairy herds

The objectives of this study were to determine the individual animal and herd level prevalence of excessive negative energy balance (eNEB) in commercial UK dairy herds. Between April 2006 and March 2015, blood samples from 84,369 individual cows from 1748 different UK farms were received by a commercial laboratory service specializing in dairy cow nutritional monitoring. Following removal of all potential duplicate cows, the final dataset comprised 69,161 unique individual cows. The prevalence of eNEB was determined using plasma thresholds of β-hydroxybutyrate (BHB), non-esterified fatty acids (NEFA) and glucose.Overall prevalence of subclinical ketosis (SCK) in the first 20 days of lactation was 28.5%, 17.3% and 11.7% using BHB thresholds of 1.0, 1.2 and 1.4 mmol/L respectively. Prevalence of NEFA values ≥0.5 mmol/L in the last 10 days prior to calving was 26.0%, and 40.3% of cows had NEFA values ≥0.7 mmol/L in the first 20 days in milk (DIM). Combining BHB, NEFA and glucose showed that 52.0% of cows had one or more of the three biochemical measures of energy balance outside the respective threshold value in the last 10 days pre-calving, and 75.2% of cows showed a similar biochemical pattern in the first 20 DIM. The median herd prevalence of elevated BHB and/or NEFA was 37.5% in late pregnancy and 59.8% in the first 20 DIM, with substantial herd variation. Using multiple measures for the assessment of energy balance, this study has shown that eNEB affects substantial numbers of UK dairy cows.

Bovine tuberculosis in Eastern Ethiopia: prevalence, risk factors and its public health importance

Bovine tuberculosis is among the primary zoonotic disease caused by Mycobacterium bovis. A cross-sectional study was conductedon 315 cattle in selected areas of eastern Ethiopia, aiming to estimate the occurrence of bovine tuberculosis using comparative intradermal tuberculin skin test and assess cattle owners’ awareness on its public health implication. Random sampling method was applied in order to select animals from farm/household. Forty three farm/household owners of tuberculin tested animals were interviewed using pre-tested structured questionnaires. The overall prevalence of bovine tuberculosis was 20.3 % (n=64) in dairy cattle at recommended cut off >4 mm. From a total of 43 farms/households tested, 22 were positive; each farm exhibited at least one tuberculin positive reactor animal with a total herd level prevalence of 51.2 %. The prevalence of bovine tuberculosis in individual animal level was significantly different (χ2=45.2; P-value <0.001) in different sites. Farming system, herd size and other risk factors were significantly (P<0.05) associated with bovine tuberculosis occurrence. Of the total interviewed farm owners, only 33 % had the knowledge of or had heard about bovine tuberculosis and 23 % respondents were aware of the zoonotic importance of the disease. More than 50 % of the interviewees had shown their preference of raw milk consumption. The study showed bovine tuberculosis is highly prevalent. The majority of cattle owners lack awareness about the disease and its public health significance. Awareness rising about the disease, its transmission and zoonotic implication is of great importance for reduction and control measures.

Evaluation of test-day milk somatic cell count information to predict intramammary infection with major pathogens in dairy cattle at drying off

The objectives of this study were (1) to determine the test characteristics and predictive values of cow-level milk somatic cell count (SCC) information from (multiple) test-day recordings before drying off to identify major-pathogen-infected cows at drying off; and (2) to explore to what extent (an estimate of) the herd prevalence of subclinical mastitis, milk yield level, and parity of the cows affects the estimates. In total, 550 cows from 15 commercial dairy herds with overall good udder health management were dried-off during a study period of 6 mo. Test-day SCC were available through milk recording and within 5 d before drying off cows were sampled for quarter-level bacteriological culturing serving as the gold standard. Sensitivity (Se), specificity (Sp), positive predictive value (PPV), and negative predictive value (NPV) were calculated at different threshold values of SCC, ranging between 50,000 and 500,000 cells/mL, to detect major-pathogen-infected cows. At a commonly used threshold of 200,000 cells/mL, the Se and Sp of (a combination of) test-day SCC before drying off ranged between 37.6 and 57.6% and between 66.7 and 79.3%, respectively. Still, estimates were modified by the herd level prevalence of subclinical mastitis and the cow's milk yield and parity. For instance, at the 200,000 cells/mL threshold using the geometric mean SCC of the 3 last test-days, the overall Se, Sp, PPV, and NPV were 37.6, 79.3, 30.8, and 83.9%, respectively, whereas these were 27.8, 87.5, 21.7, and 90.6%, respectively, for heifers and 40.3, 73.5, 33.3, and 78.9%, respectively, for multiparous cows. In conclusion, test-day SCC records obtained via milk recording are reliable to detect dairy cows at drying off that are not infected with major pathogens as determined by bacteriological culture and could eventually facilitate implementation of selective dry cow therapy in commercial dairy herds. Because estimates of the herd-level prevalence of subclinical mastitis, milk yield level, and parity of the cows affect the estimates of the test characteristics and predictive values to some extent, one should consider taking these parameters into account when differentiating infected from uninfected cows based on SCC data.

Estimating the herd and cow level prevalence of bovine digital dermatitis on New Zealand dairy farms: A Bayesian superpopulation approach

A cross-sectional study of 127 dairy herds distributed across four regions of New Zealand (NZ) was conducted to estimate the regional herd-level prevalence of bovine digital dermatitis (BDD) and the prevalence of cows with BDD lesions within affected herds. Each herd was visited once during the 2016–2017 lactating season and the rear feet of all cows in the milking herd were examined to detect the presence of BDD lesions. Of the 127 herds examined, 63 had at least one cow with a detected BDD lesion. Of the 59 849 cows observed, 646 cows were observed with BDD lesions. All of the herds in which BBD was detected were located in three of the four regions (Waikato, Manawatu and South Canterbury). No convincing lesions were observed on the West Coast. The probability of BDD freedom on the West Coast was predicted to be 99.97% using a Bayesian latent class model. For the three regions where BDD lesions were observed, the true herd level and cow level prevalences were estimated using a Bayesian superpopulation approach which accounted for the imperfect diagnostic method. Based on priors obtained from previous research in another region of NZ (Taranaki), the true herd level prevalences in Waikato, Manawatu and South Canterbury were estimated to be 59.2% (95% probability interval [PI]: 44.3%–73.9%), 43.3% (95%PI: 29%–59%) and 65.9% (95%PI: 49.5%–79.9%), respectively, while the true median within-herd prevalences were estimated as 3.2% (95%PI: 2%–5%), 1.7% (95%PI: 0.9%–3.1%) and 3.7% (95%PI: 2.4%–5.5%), respectively. All of these estimates except for the true herd level prevalence in Manawatu were fairly robust to changes in the priors. For Manawatu region, changing from the prior obtained in Taranaki (the best estimate of the herd level prevalence = 60%, 95% sure > 40%) to one where the mode was 50% (95% sure < 80%) reduced the posterior from 43.3% to 35.2% (95%PI: 20.1%–53.5%). The marked variation in BDD prevalence between regions and between farms highlights the need for further exploration into risk factors for disease.

Bovine tuberculosis in eastern Ethiopia: prevalence, risk factors and its public health importance

BackgroundBovine tuberculosis is among the primary zoonotic disease caused by Mycobacterium bovis which has significant impact on the health of livestock and human. It has been significantly a cause for great economic loss in animal production.MethodologyA cross-sectional study was conducted from December 2014 to June 2016 on 315 cattle in selected areas of eastern Ethiopia, aiming to estimate the occurrence of bovine tuberculosis using comparative intradermal tuberculin skin test and assess cattle owners’ awareness on its public health implication. Random sampling method was applied in order to select animals from farm/household and associated risk factors were recorded before purified protein derivative (PPD) injection. Forty three farm/household owners of tuberculin tested animals were interviewed using pre-tested structured questionnaires.ResultsThe overall prevalence of bovine tuberculosis was 20.3% (n = 64) in dairy cattle at recommended cut off > 4 mm. From a total of 43 farms/households tested, 22 were positive; each farm exhibited at least one tuberculin positive reactor animal with a total herd level prevalence of 51.2%. The prevalence of bovine tuberculosis in individual animal level was significantly different (χ2 = 45.2; P-value = 0.000) in different sites with a higher prevalence (50%) in Dire Dawa. Farming system, herd size and other risk factors were significantly (p < 0.05) associated with bovine tuberculosis occurrence. Of the total interviewed farm owners, only 33% had the knowledge of or had heard about bovine tuberculosis and 23% respondents were aware of the zoonotic importance of the disease. More than 50% of the interviewees had shown their preference of raw milk consumption. Out of the total interviewed households, 3 (7%) farm workers had TB cases that had direct contact with the animals.ConclusionThe study showed bovine tuberculosis is highly prevalent. Associated risk factors contributed to the prevalence of the disease in cattle and its transmission. Moreover, the majority of cattle owners lack awareness about the disease and its public health significance. Awareness rising about the disease, its transmission and zoonotic implication is of great importance for reduction and control measures. Evidence of tuberculosis patient farm attendants calls also for further detail investigation.

Prevalence and risk factors of Mycoplasma bovis infection in dairy farms in northern Japan

Mycoplasma mastitis is a dairy herd health problem with growing concern in Japan. To complement the lack of epidemiological knowledge of the disease, we conducted estimation of herd-level prevalence and risk factor analysis for Mycoplasma bovis (M. bovis) mastitis using data collected from Tokachi region, one of the nation's largest milk producing area, in Hokkaido Prefecture in 2015. The herd-level prevalence was estimated at 3.8% (95% confidence interval (CI): 2.6%, 5.4%) across the region with municipality-specific prevalence ranging from 0% to 14.3%.In this study, identified risk factors for the presence of with M. bovis infection on farms were corporation-type farms and purchased cattle, after controlling for the herd size. Corporation-type farms may reflect higher frequencies of moving cows and fomites to and from other farms, which increases the risk of pathogen introduction. Purchased cattle was considered as one of the major pathways of the disease incursion, and this finding highlighted the importance of more stringent separation or quarantine protocols when introducing cattle from outside in Tokachi region. Due to the limited information available in this study and inherent nature of the study designs, these results should be interpreted with caution and further research is needed.

Low accuracy of Bayesian latent class analysis for estimation of herd-level true prevalence under certain disease characteristics—An analysis using simulated data

Estimation of the true prevalence of infected individuals involves the application of a diagnostic test to a population and adjusting according to test performance, sensitivity and specificity. Bayesian latent class analysis for the estimation of herd and animal-level true prevalence, has become increasingly used in veterinary epidemiology and is particularly useful in incorporating uncertainty and variability into analyses in a flexible framework. However, the approach has not yet been evaluated using simulated data where the true prevalence is known. Furthermore, using this approach, the within-herd true prevalence is often assumed to follow a beta distribution, the parameters of which may be modelled using hyperpriors to incorporate both uncertainty and variability associated with this parameter. Recently however, the authors of the current study highlighted a potential issue with this approach, in particular, with fitting the distributions and a tendency for the resulting distribution to invert and become clustered at zero. Therefore, the objective of the present study was to evaluate commonly specified models using simulated datasets where the herd-level true prevalence was known. The specific purpose was to compare findings from models using hyperpriors to those using a simple beta distribution to model within-herd prevalence. A second objective was to investigate sources of error by varying characteristics of the simulated dataset. Mycobacterium avium subspecies paratuberculosis infection was used as an example for the baseline dataset. Data were simulated for 1000 herds across a range of herd-level true prevalence scenarios, and models were fitted using priors from recently published studies. The results demonstrated poor performance of these latent class models for diseases characterised by poor diagnostic test sensitivity and low within-herd true prevalence. All variations of the model appeared to be sensitive to the prior and tended to overestimate herd-level true prevalence. Estimates were substantially improved in different infection scenarios by increasing test sensitivity and within-herd true prevalence. The results of this study raise questions about the accuracy of published estimates for the herd-level true prevalence of paratuberculosis based on serological testing, using latent class analysis. This study highlights the importance of conducting more rigorous sensitivity analyses than have been carried out in previous analyses published to date.

Short communication: Validation of a test-day milk test for β-hydroxybutyrate for identifying cows with hyperketonemia

Subclinical ketosis is a common metabolic disorder affecting dairy cattle that results in a greater risk for the development of subsequent metabolic and infectious disease. Canwest Dairy Herd Improvement (DHI; Guelph, ON, Canada) has begun to use an infrared test (MilkoScan FT600, Foss Analytical A/S, Hillerød, Denmark) applied to metered composite milk samples to detect β-hydroxybutyrate (BHB) levels as a herd surveillance test for hyperketonemia. However, the test has not been compared with the gold standard, serum BHB as determined in a reference diagnostic laboratory. The objective of this cross-sectional diagnostic accuracy study was to validate the DHI milk BHB test to identify cows with hyperketonemia as determined by quantification of BHB in serum. A total of 316 cows from 17 dairy herds in southwestern Ontario had a milk and blood sample taken. Milk was collected at a routine DHI test, and blood from the same cow was sampled within 24 h of the milk test. The BHB concentration in milk was determined using the DHI milk BHB test, and serum was sent to the Animal Health Laboratory at the University of Guelph (Guelph, ON, Canada). A nonparametric receiver operating characteristic curve was generated to compare DHI milk BHB concentrations with serum BHB concentrations. Overall, a total of 34 cows (11%) had a level of serum BHB ≥1.2 mmol/L. The concentration of DHI milk BHB was moderately correlated with the concentration of serum BHB, yielding a coefficient of determination value of 0.61. The optimal cut point for determining hyperketonemia (≥1.2 mmol/L) on the DHI milk BHB test was ≥0.14 mmol/L, yielding a sensitivity of 81% and specificity of 92%. The performance of the DHI milk BHB test varied depending on the days in milk (DIM) of the cows tested, with a higher specificity being found in cows that were ≤25 DIM compared with cows tested >25 DIM. If the herd-level prevalence of hyperketonemia was ≥14%, the DHI milk BHB test had an improved sensitivity when compared with a herd-level prevalence of <14%. This study demonstrates that the DHI milk BHB test is a reliable measure for evaluating hyperketonemia using routine DHI milk samples and could be used as a herd-level monitoring tool for ketosis when evaluating nutritional management or preventative medicine strategies.

Prevalence of Bovine Leukemia Virus Antibodies in US Dairy Cattle.

Objective To estimate current US herd-level and animal-level prevalence of bovine leukemia virus (BLV) in dairy cows and characterize epidemiologic features. Design Cross-sectional observational study design and survey. Animals 4120 dairy cows from 103 commercial dairy herds in 11 states across the US. Procedures Milk samples were collected from dairy cows through routine commercial sampling and tested for anti-BLV antibodies by antibody capture ELISA. Based on the ELISA results of a sample of an average of 40 cows per herd, within-herd apparent prevalence (AP) was estimated by a directly standardized method and by a lactation-weighted method for each herd. Within-herd AP estimates were summarized to give estimates of US herd-level and animal-level AP. Differences in AP by lactation, region, state, breed, and herd size were examined to characterize basic epidemiologic features of BLV infection. Results 94.2% of herds had at least one BLV antibody positive cow detected. The average within-herd standardized AP was 46.5%. Lactation-specific AP increased with increasing lactation number, from 29.7% in first lactation cows to 58.9% in 4th and greater lactation cows. Significant differences were not observed based on region, state, breed, or herd size. Conclusions and Clinical Relevance These results are consistent with a historical trend of increasing prevalence of BLV among US dairy cattle. Given the findings of other studies on the negative impacts of BLV infection on milk production and cow longevity, these findings are clinically relevant for veterinarians counseling dairy clients on the risks of BLV to their herds.

Risk factors for subclinical hypocalcaemia, and associations between subclinical hypocalcaemia and reproductive performance, in pasture-based dairy herds in New Zealand

AIMSTo estimate the herd-level prevalence of subclinical hypocalcaemia within 3 days of calving, to determine cow and herd-level risk factors for this condition, and associations with reproductive performance, in pasture-based cows in New Zealand.METHODSBetween 10 and 15 clinically healthy cows ≥3-years-old (n=1,051) were enrolled from 76 spring-calving dairy herds. Blood samples were collected from all cows on 1 or 2 days within 3 days of calving, and assayed for total concentrations of Ca in serum. Subclinical hypocalcaemia was defined as concentrations of Ca in serum ≤2.14 mmol/L, and herd-level prevalence was the percentage of sampled cows with subclinical hypocalcaemia. Breeding and pregnancy diagnosis data were obtained for each cow to calculate reproductive outcomes. Herd-level data about management practices were collected from farmers at enrolment. Associations between cow-level variables, and reproductive outcomes, and subclinical hypocalcaemia were examined using multivariable logistic regression mixed models. Associations between herd-level variables and prevalence of subclinical hypocalcaemia were examined using a multivariable linear regression model.RESULTSMean herd-level prevalence of subclinical hypocalcaemia was 52 (95% CI=49–55)%. Risk of subclinical hypocalcaemia at the cow-level was associated with an interaction between age of cow and interval from calving to sampling (p=0.03). Increasing age of cow was associated with increased risk of subclinical hypocalcaemia, and cows sampled on the day of calving had an increased risk compared with cows sampled 1 or 2 days after calving. Increased herd-level prevalence of subclinical hypocalcaemia was associated with feeding grass silage (p=0.06) or maize silage (p=0.004), and feeding increasing amounts of elemental Mg in the form of magnesium oxide (p=0.02). The mean farmer-reported herd-level prevalence of clinical hypocalcaemia was 2.9 (95% CI=2.1–3.8)%. Subclinical hypocalcaemia was not associated with any of the reproductive outcomes measured.CONCLUSIONS AND CLINICAL RELEVANCEThere was a high prevalence of subclinical hypocalcaemia in the pasture-fed, spring-calving dairy herds sampled and a large between-herd variation in prevalence. Subclinical hypocalcaemia increased with increasing age, and declined with time postpartum. Herd-level prevalence was associated with feeding grass silage and maize silage to pre-calving cows and with increasing amounts of supplemented magnesium oxide. Subclinical hypocalcaemia was not associated with reproductive outcomes.

Seroprevalence and risk factors of lumpy skin disease in Ethiopia

Lumpy skin disease (LSD) is an acute or inapparent viral disease of cattle which is endemic in many African and Middle East countries. LSD is one of the major transboundary livestock diseases in Ethiopia. A cross-sectional study using multistage cluster sampling was undertaken in central and north-western parts of Ethiopia with the objectives to estimate seroprevalence and to identify and quantify risk factors contributing to the occurrence of the disease. A total of 2386 cattle sera were sampled from 605 herds and 30 clusters (kebeles) located in 10 districts and tested for presence of LSD virus antibodies using virus neutralization test. All the serum samples were collected from cattle having no history of LSD vaccination. The overall animal level and herd level apparent seroprevalences were 25.4% (95% CI: 23.7–27.2) and 48.9% (95% CI: 44.9-52.9), respectively and varied significantly between districts. The true animal level and herd level prevalences were estimated as 26.5% (95% CI: 24.7–28.3) and 52.6% (95% CI: 48.3–56.9), respectively. At animal level, adult age (OR = 2.44 (95% CI: 1.67–3.55) compared to calf), contact with other animals (OR = 0.41 (95% CI: 0.23-0.74), compared to no contact) and presence of water bodies (OR = 1.61 (95% CI: 1.03–2.52), compared to no such bodies) were identified as the most important risk factors in relation to testing LSD positive. The putative risk factors altitude, breed, sex, and presence of animal trade route showed no significant association with LSD sero-status. Generally, cattle population with many adult animals and that live in wet areas are at highest risk, whereas cattle in frequent contact with other animals and animal species have lower risk, potentially due to a dilution effect of vectors.

Epidemiological situation of vesicular stomatitis virus infection in cattle in the state of Paraíba, semiarid region of Brazil

The aim of this survey was to estimate the apparent herd-level and animal-level prevalences, as well as to identify risk factors and spatial clustering of vesicular stomatitis virus (VSV) positive herds in the state of Paraíba, semiarid of Brazil. The state was divided into three sampling strata: Sertão, Borborema and Zona da Mata/Agreste. For each sampling stratum, herd-level and animal-level prevalences were estimated by a two-stage sampling survey. First, a pre-established number of herds (primary sampling units) were randomly selected; second, within each herd, a pre-established number of cows aged ≥ 24 months were systematically selected (secondary sampling units). In total, 2279 animals were sampled from 468 herds. Serum samples were submitted to virus neutralization (VN) test for detection of antibodies to VSV using three viral strains: VSIV-3 2013SaoBento/Paraiba E, strain Indiana (VSIV-1) and VSNJV. A herd was considered positive for VSV if it included at least one positive animal in herds of up to 10 females, two positive animals in herds of 11–99 females, and three positive in herds with more than 99 females. The spatial clustering was assessed using the Cuzick–Edwards’ k-nearest neighbor method and spatial scan statistics. The apparent herd-level prevalence in the state of Paraíba was 38.5% (95% CI = 35.5–41.6%), 80.6% (95% CI = 73.6–86.2%) in the region of Sertão, 7.0% (95% CI = 3.9–12.2%) in Borborema, and 2.6% (95% CI = 1.0–6.7%) in Agreste/Zona da Mata. The apparent animal-level prevalence was 26.2% (95% CI = 20.6–32.8%) in the state of Paraíba, 48.2% (95% CI = 41.5–54.9%) in Sertão, 6.3% (95% CI = 2.7–14%) in Borborema, and 3.2% 1.9% (95% CI = 0.4–8.4%) in Agreste/Zona da Mata. The risk factors identified were as follows: mixed production (milk/beef) (OR = 4.54), herd size > 23 animals (OR = 3.57), presence of cervids (OR = 15.24), rental of pastures (OR = 3.02), sharing of water sources (OR = 2.57) and presence of horses (OR = 1.69). Two significant clusters of positive herds were detected: the primary cluster covered the Sertão region and the secondary cluster covered part of the Sertão and Borborema regions. Our results suggest high VSV circulation in the bovine population of the state of Paraíba, semiarid region of Brazil, mainly in the Sertão mesoregion, and based on risk factor analysis it was possible to identify important associations that deserve more investigation on causal factors.

Seroprevalence and herd-level risk factors for seroprevalence of Leptospira spp. in sheep, beef cattle and deer in New Zealand

AIMSTo determine seroprevalence of Leptospira borgpetersenii serovar Hardjo and L. interrogans serovar Pomona in beef cattle, sheep and deer in New Zealand and the association between farm-level risk factors and seroprevalence.METHODSBetween June 2009 and July 2010, 20 serum samples per flock or herd were collected from 162 sheep flocks, and 116 beef cattle and 99 deer herds from 238 farms, along with farm data by interview. Samples were tested for antibodies to serovars Hardjo and Pomona by microscopic agglutination testing, with a titre ≥48 being positive. Species-specific associations between herd-level seroprevalence (number of seropositive animals, for each serovar, divided by the number of animals tested) and herd-level risk factors were determined by multivariable logistic regression analysis. Vaccinated animals were excluded from seroprevalence estimates but included in multivariable analyses.RESULTSFor sheep (n=3,339), animal-level seroprevalence was 43.6 (95% CI=41.9–45.3)% for serovar Hardjo and 14.1 (95% CI=12.9–15.3)% for serovar Pomona; for beef cattle(n=1,886), it was 45.6 (95% CI=43.3–47.9)% for Hardjo and 19.6 (95% CI=17.9–21.5)% for Pomona; and for deer (n=1,870), it was 26.3 (95% CI=24.3–28.4)% for Hardjo, 8.8 (95% CI=7.6–10.2)% for Pomona.In sheep flocks (n=161), flock-level prevalence for Hardjo varied from 77.9–91.3%, and for Pomona from 40.4–73.9%, when ≥1, ≥2 or ≥3 animals were seropositive. In beef herds (n=95), herd-level prevalence for Hardjo varied from 79.0–90.5%, and for Pomona from 42.1–68.4%. In deer herds (n=93), herd-level prevalence for Hardjo varied from 45.2–59.1%, and for Pomona from 22.6–48.4%.For sheep flocks, herd-level seroprevalence for Hardjo was associated with flock size (OR=1.56) and number of dogs (OR=0.75), and for Pomona, seroprevalence varied with region. For beef cattle, herd-level seroprevalence for Hardjo was associated with herd size (OR=1.4), presence of dams (OR=0.6) and vaccination (OR=2.9), and for Pomona, co-grazing with deer (OR=0.4), vaccination (OR=3.22), presence of dams (OR=0.2) and streams (OR=2.7). For deer herds, seroprevalence for Hardjo or Pomona was associated with herd size (OR=1.6 and 1.8) and varied with region, and for Pomona seroprevalence varied with season (summer vs. winter: OR=4.8).CONCLUSIONSSerovars Hardjo and Pomona were highly prevalent at herd and animal levels, with serovar Hardjo highest in all species. Larger herd size was the common risk factor for seroprevalence in all livestock species.

Herd-level prevalence of Salmonella Dublin among New York dairy farms based on antibody testing of bulk tank milk.

Salmonella Dublin is an important cause of salmonellosis among dairy cattle and poses a considerable threat to public health. This serotype is increasingly being identified among bovine Salmonella isolates from clinical samples in the north-eastern United States, and these isolates are generally multidrug resistant. Our objective was to estimate the herd-level prevalence of Salmonella Dublin among dairy cattle herds throughout New York. Bulk tank milk samples from nearly all commercial dairy herds in New York were collected from milk quality testing laboratories during the first half of 2013. Antibody testing of bulk tank milk was performed using a Salmonella Dublin ELISA kit. Samples representing 4,896 commercial dairies were collected, and antibodies against Salmonella Dublin were detected in 46 herds (0.9%; 95% CI, 0.7%-1.3%). Given the herd-level sensitivity of ELISA testing for Salmonella Dublin in bulk tank milk at a single timepoint, this approach presumably underestimated the true prevalence. Some Salmonella Dublin-positive herds had both positive and negative bulk tanks at the same sampling time, indicating that herds with multiple tanks should test all of them when using this ELISA. Further research is needed to better understand the epidemiologic features of Salmonella Dublin in the north-eastern United States, including risk factors for introduction into dairy herds and principal transmission pathways.

Herd-level prevalence of Johne's disease and BVD, management practices and farm characteristics for positive dairy herds in Utah and Idaho

Johne's disease (JD) and bovine viral diarrhea (BVD) are expensive dairy cattle diseases causing production, infertility, and death losses. Herd-level prevalence estimates are 68% for JD and 15% for BVD. The objectives of this study were to estimate regional dairy herd-level prevalence of JD and BVD and evaluate farm characteristics, management, and control practices on farms with either disease detected.