Foot and mouth disease in the Borana pastoral system,southern Ethiopia and implications for livelihoods and international trade

Participatory epidemiology (PE) was used on the Borana plateau of southern Ethiopia to understand pastoralist’s perceptions of the clinical and epidemiological features of foot and mouth disease (FMD) in cattle. Matrix scoring showed good agreement between informant groups on the clinical signs of acute and chronic FMD, and findings were cross-checked by clinical examination of cattle and assessment of previous clinical FMD at herd level by detection of antibody to non structural proteins of FMD virus. The positive predictive value of pastoralist’s diagnosis of FMD at herd level was 93.1%. The annual age-specific incidence and mortality of acute FMD in 50 herds was estimated using proportional piling. The estimated mean incidence of acute FMD varied from in 18.5% in cattle less than two years of age to 14.0% in cattle three to four years of age. The estimated mean mortality due to acute FMD varied from 2.8% in cattle less than two years of age to 0.3% in cattle three of age or older. Pearson correlation coefficients for acute FMD by age group were −0.12 (p > 0.05) for incidence and −0.59 (p < 0.001) for mortality. Estimates of the annual incidence of chronic FMD varied from 0.2% in cattle less than two years of age to 1.8% in cattle three to four years of age. The Pearson correlation coefficient for the incidence of chronic FMD by age group was 0.47 (p < 0.001). Outbreaks of FMD peaked in Borana cattle during the two dry seasons and were attributed to increased cattle movement to dry season grazing areas. The mean seroprevalence of FMD was estimated at 21% (n = 920) and 55.2% of herds (n = 116) tested seropositive. Serotyping of 120 seropositive samples indicated serotypes O (99.2%), A (95.8%), SAT 2 (80%) and C (67.5%). The endemic nature of FMD in Borana pastoral herds is discussed in terms of the direct household-level impact of the disease, and the increasing export of cattle and chilled beef from Ethiopia.     

Dynamics of bovine herpesvirus type 1 infection in Estonian dairy herds with and without a control programme

Bovine herpesvirus type 1 (BHV-1) is an important bovine pathogen, exacerbating poor health and the productivity of cattle. The aims of this study were to detect the efficacy of vaccination programmes in lowering the seroprevalence of BHV-1 gE within the dairy herd and to follow the dynamics of the infection in non-vaccinated herds with uninfected heifers. A two-year longitudinal study was carried out on seven herds that were vaccinated, and in five herds with uninfected heifers without applying a control programme. After the start of the vaccination programme, calves born remained free from the virus. However, in one herd, 7 per cent (95 per cent CI 2 to 18) of these animals showed antibodies to BHV-1 two years after the first vaccination. A decline in BHV-1 antibody prevalence was found in vaccinating herds. Among the five herds not under the control programme, one experienced active virus spread, although one herd experienced self-clearance of the virus. In the herds with high BHV-1 prevalence, vaccinating all cattle from three months of age twice a year with a commercial inactivated marker vaccine efficiently protected offspring from becoming infected, and lowered the prevalence of BHV-1 within the herd. A small proportion of herds may experience self-clearance of the virus.     

A seroepidemiological study of bovine pestivirus in Queensland beef and dairy herds conducted in 1994/95

OBJECTIVE: To describe the distribution and prevalence of cattle herds with detectable antibody to bovine pestivirus in Queensland in 1994/95. MATERIALS AND METHODS: The study used 7,838 serum samples collected from 250 herds in Queensland, as part of a structured animal health surveillance program conducted in 1994 and 1995. Samples were collected from female cattle bred on the property. In each herd, 10 to 20 heifers less than two years of age and 10 to 15 older cows were sampled giving a 95% probability of detecting one or more seropositive animals if the seroprevalence was approximately 10% or greater. Sera were analysed for antibodies to bovine pestivirus using a virus neutralisation test. RESULTS: Total cattle numbers in sampled herds varied from 62 to 24,600 head, while total area of properties sampled varied from 50 to 395,400 hectares. Eleven percent of herds contained no seropositive animals among those sampled, and in 38% of herds, all sampled cattle aged one to two years of age were seronegative. There was a trend for larger herds to have one or more animals seropositive for bovine pestivirus (chi-squared for Linear trend = 3.656, p = 0.056). Herds with more than 500 head of cattle were significantly more likely than herds with less than 500 head to contain one or more seropositive animals in any age group (prevalence ratio = 1.12; 95% confidence interval 1.01 - 1.23; p = 0.026). Age specific seroprevalence increased from around 10% in heifers, to between 75% and 85% in cows aged 10 years. The average annual incidence risk for bovine pestivirus infection varied from 0.12 to 0.24 seroconversions per cattle year at risk, and did not vary with age. The overall crude seroprevalence adjusted for herd size was 45%. There was a wide range of seroprevalence recorded for each level of stocking intensity. CONCLUSIONS: This survey provides valuable baseline data on bovine pestivirus infection in Queensland cattle herds.     

Bluetongue infections in Louisiana cattle

Bluetongue virus (BTV) serotype 17 was isolated from cattle with clinical signs of bluetongue disease during 1978 and 1979 epizootics. Bovine sera from 6 herds located in an epizootic region were examined in 1979 for antibodies, using an immunodiffusion (ID) test. Of 300 sera, 164 (54.7%) were seropositive. Sera from statewide surveys of Louisiana cattle in July to August 1980 and December 1980 to January 1981 were tested for BTV antibodies, using the ID test. Fifty-eight of 70 herds (82.9%) and 164 of 597 (27.5%) individual cattle tested in July to August 1980 were seropositive. Fifty-four of 63 (85.7%) herds and 170 of 600 (28.3%) individual cattle tested in December 1980 to January 1981 were seropositive. Significant differences (P less than 0.01) were found in the seropositive rates between the various geographic regions of the state during each survey. Adult breeding-age cattle in 3 sentinel herds were tested for BTV antibodies beginning in 1976 and continuing through January 1981. During this interval, the seropositive rate in 2 of 3 herds was increased. Also, individual cattle in all 3 of these herds converted from seronegative to seropositive, indicating exposure during a particular interval for each herd. The age distribution of seropositive cattle in a dairy indicated that 2-year-old cattle had a seropositive rate comparable with that of older animals in the herd, suggesting that the 2-year-old animals had been exposed to a BTV before they entered the breeding herd.     

Evaluation of bluetongue virus diagnostic tests in free-ranging bighorn sheep

Five bluetongue virus (BTV) diagnostic tests were evaluated for use in free-ranging bighorn sheep. We sampled one bighorn sheep population four times between 1989 and 1995. The tests evaluated included virus isolation (VI), polymerase-chain reaction (PCR), serum neutralization (SN), agar-gel immunodiffusion (AGID), and competitive enzyme-linked immunosorbent assay (c-ELISA). The c-ELISA, AGID and SN tests had high levels of agreement in determining serogroup exposure in bighorn sheep. We used maximum-likelihood algorithms to estimate the parameters of each diagnostic test used. Although the c-ELISA and AGID had high sensitivity and specificity, the SN had perfect specificity but lower apparent sensitivity. Due to the potential of cross-reactions among multiple serotypes, results of the SN must be interpreted with caution when assessing serotype exposure in an area where multiple serotypes are endemic. The PCR assay delineated convalescent antibody titers from more-recent infections, and consequently, was pivotal in distinguishing a different exposure pattern between the bighorn sheep and cattle in an adjacent herd. Based on an increasing seroprevalence (50% to 100%), BTV circulated through this bighorn sheep population between 1989 and 1993. This increase in seroprevalence coincided with a bighorn die-off due to BTV infection in June, 1991. An adjacent cattle herd was sampled in 1995 for comparison. The bighorn sheep and adjacent cattle had different patterns of exposure to BTV between 1994 and 1995. There was no evidence that BTV circulated through the bighorn sheep population from 1994 to 1995. In 1995, seroprevalence to BTV decreased to 72%, none of yearling bighorn was seropositive, and all of the 39 bighorn sheep were PCR-negative. In contrast, all adult cattle were seropositive to BTV by c-ELISA and SN, and 4 of the calves were seropositive; 11 of the 24 cattle were PCR-positive, including all five calves. Overall, the pattern of temporal herd immunity in the bighorn sheep appeared to follow a classic epidemic curve, with the appearance and subsequent disappearance of herd immunity coinciding with the 1991 die-off in this population. As low levels of herd immunity and high proportions of susceptible animals are key factors in the development of epidemics, this population of bighorn sheep may be at increased risk for a BTV epidemic in the future.     

Seroprevalence of bluetongue serotype 8 in cattle in the Netherlands in spring 2007, and its consequences

A cross-sectional study was carried out in spring 2007, at the end of the first bluetongue outbreak season, to determine the geographical spread of bluetongue virus serotype 8 (btv-8) infection in cattle in the Netherlands and the consequences for some production parameters. Blood samples from cattle submitted to the laboratory of the Dutch Animal Health Service for other voluntary and obligatory health programmes were tested serologically for btv-8. In total, 37,073 samples were tested and 659 (1.78 per cent) were seropositive. The samples came from 5436 herds, of which 45 per cent of herds had only one sample submitted from them. The prevalence was highest in the south of the country, where the outbreak had started, and decreased towards the north. In 340 herds more than 50 per cent of cattle were tested, of which 156 herds were located in infected compartments, and in 37 of these herds (10.9 per cent) at least one positive cow was detected. The average within-herd prevalence in the 37 herds was 39.3 per cent: 2.2 per cent in 11 dairy herds, 68.4 per cent in 20 small-scale herds and 14 per cent in four suckler cow herds. The prevalence differed significantly between herd types but did not show a geographical trend. The average net return for milk production amounted to euro2417/cow/year and it decreased significantly on average by euro48/cow/year in the bluetongue-infected dairy herds during the bluetongue period. On the small-scale farms, the incidence of mortality increased by 3.2 (95 per cent confidence interval [CI] 1.2 to 9.1) times in the infected herds during the bluetongue period, but the voluntary culling rate decreased by a factor of 2.3 (95 per cent CI 1.1 to 4.8).     

Leptospiral antibodies in the breeding goat population of Poland

In 2007, a survey was conducted on the prevalence of antibodies to 19 Leptospira serovars in goats in Poland . Sera were collected from adult females of all 49 breeding goat herds in Poland by applying simple random sampling. In total, 736 sera were tested by the microscopic agglutination test. A herd was considered seropositive if at least one goat with a titre of 100 or more was detected. Herd-level seroprevalence of Leptospira was 89.8 per cent and individual-level seroprevalence varied from less than 1.0 to 85.0 per cent among the herds. Antibodies to Leptospira serovars Zanoni, Bratislava, Autumnalis, Australis and Javanica were most frequently detected. Although 40.3 per cent of seropositive goats had high antibody titres (≥ 400), suggesting recent infection, no relationship with abortions or other clinical manifestation of leptospirosis in goats was detected.     

Infection of cattle by airborne foot-and-mouth disease virus: minimal doses with O1 and SAT 2 strains

Equipment has been constructed and methods developed for exposing individual cattle to two strains of foot-and-mouth disease (FMD) virus in aerosols to determine the minimal infective dose by the respiratory route. The aerosols used were produced either artificially by a spinning-top aerosol generator, in which case they were of homogeneous small particle size (less than 3 micron in diameter) or else they were derived naturally from infected pigs, in which case the particles were heterogeneous in size. Two strains of FMD virus were used: an O1 strain of UK origin and a SAT 2 strain from South Africa. The lowest doses which initiated infection were 12.5 TCID50 of O1 BFS virus and 25 TCID50 of SAT 2 virus, infectivity having been assayed in primary bovine thyroid cell cultures. Following exposure to low doses of virus (range 12 to 316 TCID50) 33 per cent of the cattle exposed to O1 BFS virus and 27 per cent exposed to SAT 2 virus were infected but did not develop detectable vesicular lesions.     

Herd-specific and age-specific seroprevalence of Neospora caninum in 14 British dairy herds.

All the cattle in 14 dairy herds in England were tested for Neospora caninum-specific antibodies with a commercial ELISA. Three of the herds had had sporadic abortions, eight had had endemic abortions and three had had epidemic abortions associated with N caninum before the study. Of 4295 cattle tested, 17.1 per cent were seropositive and the herd-specific prevalence ranged from 7.3 per cent to 44.8 per cent. No significant effect of either herd size (P = 0.988), endemic (P = 0.869) or epidemic (P = 0.138) patterns of abortion on herd-specific prevalence was found by using logistic regression analysis. There was no evidence in any herd of a significant increase in prevalence with age; the prevalence in seven-to 12-month-old cattle was not significantly different (P > 0.400) from the prevalence in older cattle, except that there was a significantly lower prevalence (P = 0.017) in 13-to 24-month-old cattle. The results of this study are consistent with vertical transmission being the major route of N caninum transmission in these herds.     

Virological and serological evidence of bovine herpesvirus type 4 in cattle in Northern Ireland

Bovine herpesvirus type 4 (BHV-4), a member of the genus Rhadinovirus, subfamily Gammaherpesvirinae, within the family Herpesviridae, was isolated in fetal bovine lung cells from samples of vaginal discharge taken from a dairy herd in which approximately 50 per cent of the cattle developed metritis after calving. The identity of the isolate was confirmed by immunofluorescent staining with a BHV-4-specific monoclonal antibody and partial sequencing of a portion of the glycoprotein B gene. Serological testing failed to demonstrate a significant association between the exposure of the cattle to BHV-4 and the metritis, but several cattle seroconverted during the periparturient period, consistent with the recrudescence and shedding of virus associated with the stresses of parturition and the onset of lactation. Despite the previous failure to detect BHV-4 in Northern Ireland, a serological survey of 999 cattle in 49 dairy herds and 51 beef herds found widespread evidence of exposure: 29 of the dairy herds and 35 of the beef herds contained one or more seropositive cattle, and 33.3 per cent of the dairy cattle and 23.3 per cent of the beef cattle were positive.     

Seroprevalence of Neospora caninum and abortion in dairy cows in northern Spain.

The seroprevalence of Neospora caninum infection was estimated from a sample of 889 cattle from 43 dairy herds in three counties in the Asturias region of Spain. The true prevalence of infection was estimated to be 30.6 per cent (95 per cent confidence interval (CI) 27.6 to 33.6). Seropositivity was associated with abortion during the previous year (odds ratio (OR)=3.31, P<0.001) and was slightly higher among purchased cattle (37.6 per cent), than among cattle raised on the farm (29.1 per cent) (P=0.078). Seropositive cows were more likely than seronegative cows to have had a seropositive dam (OR=2.3, P=0.011), suggesting that congenital transmission contributed to about 56 per cent of the infections. Herds with a true seroprevalence above 10 per cent had more dogs on the farm, than herds with a lower prevalence (P=0.032). The ORS relating abortion to seropositivity in individual herds ranged from 0.7 to 19, indicating that some herds experienced few abortions caused by N. caninum, while others experienced more abortions due to the organism. Overall, 38.7 per cent of the abortions were estimated to have been attributable to N. caninum.     

Prevalence of paratuberculosis (Johne's disease) in the Belgian cattle population

The national bovine paratuberculosis (PTB) seroprevalence (apparent prevalence) in the Belgian cattle population was determined by a serological survey that was conducted from December 1997 to March 1998. In a random sample of herds (N=556, 9.5%), all adult cattle of 24 months of age or older (N=13,317, 0.4%) were tested for the presence of antibodies using a commercially available absorbed ELISA test kit. The PTB median within-herd seroprevalence (proportion of detected animals within the seropositive herds) and the PTB individual-animal seroprevalence (proportion of detected animals) were, respectively, 2.9% (quartiles=1.6-5.6) and 0.87% (95% confidence interval (CI)=0.71-1.03). The PTB herd seroprevalence (proportion of detected herds) was 18% (95% CI=14-21).Assuming a test sensitivity and specificity of 45 and 99% [Sweeney et al., 1995. J. Vet. Diagn. Invest. 7 (4), 488; Sockett et al., 1992. J. Clin. Microbiol. 30 (5), 1134], respectively, the median true within-herd prevalence and the true individual-animal were estimated to be 7 and 2%, respectively. The true herd prevalence of Mycobacterium paratuberculosis infection was first estimated according to currently accepted methodology. This calculation revealed that the specificity of the used test has a dramatic effect on the estimation; assuming a test sensitivity of 45% and a true within-herd prevalence of 7%, the true herd prevalence estimation decreased from 36 to 0.8% if the test specificity decreased from 99. 9 to 99%, respectively. This sensitivity analysis showed that the practical limits of the accuracy of the used screening test jeopardize the estimation of the true herd prevalence within reasonable confidence limits, because the within-herd PTB true prevalence was low.For this reason we augmented the herd specificity for herds with larger adult herd size (>5). This was done by increasing the cut-off number of positive cattle required (>/=2) to classify a herd truly positive and including herds with one positive test result if there was historical evidence of PTB (previous diagnosis and/or clinical signs). This approach resulted in an estimated true herd prevalence of M. paratuberculosis infection of 6%. The true herd prevalence for dairy, mixed and beef herds was, respectively, 10, 11 and 3%.     

Regional seroprevalence of bluetongue virus in cattle in Illinois and western Indiana

OBJECTIVE: To estimate seroprevalence of bluetongue virus (BTV) and the geographic distribution of seropositive cattle herds in Illinois and western Indiana. SAMPLE POPULATION: 10,585 serum samples obtained from cattle in 60 herds during 3 transmission seasons (2000 through 2002). PROCEDURES: In a longitudinal study, serum samples were tested for BTV antibodies by use of a competitive ELISA. Four geographic zones were created by use of mean minimum January temperature. A multivariable mixed-effects logistic regression model with a random effect for herd was used to estimate seropositive risk for zone, age of cattle, herd type, and transmission season. RESULTS: Overall, BTV antibodies were detected in 156 (1.5%) samples. Estimated seroprevalence in 2000, 2001, and 2002 was 1.49%, 0.97%, and 2.18%, respectively. Risk of being seropositive for BTV was associated with geographic zone and age. Seroprevalence increased progressively from northern to southern zones, with no evidence of BTV infection in the northernmost zone. In the southernmost zone, annual seroprevalence ranged from 8.65% to 11.00%. Adult cattle were 2.35 times as likely as juvenile cattle to be seropositive. CONCLUSIONS AND CLINICAL RELEVANCE: Overall seroprevalence was lower than has been reported for Illinois cattle. Bluetongue virus antibodies were distributed heterogeneously in this region. Only in the southernmost zone was seroprevalence consistently > 2%. Regionalization of BTV risk based on state borders does not account for such variability. Serologic data could be combined with landscape, climate, and vector data to develop predictive models of BTV risk within transitional regions of the United States.     

Prevalence of Fasciola hepatica in dairy herds in England and Wales measured with an ELISA applied to bulk-tank milk

An ELISA developed to diagnose Fasciola hepatica infection in cattle by detecting serum antibodies was adapted and validated for use with samples of bulk-tank milk. The prevalence of the infection in 61 dairy herds was established by using serum antibody levels or faecal egg counts measured in a proportion of the cows in each herd. The correlation between the results of the ELISA and the herd seroprevalence was 0.83. Using a cut-off value of 27 per cent positive, the bulk-tank ELISA identified herds in which more than 25 per cent of the cows were infected with a diagnostic sensitivity of 96 per cent (95 per cent confidence interval 89 to 100 per cent) and a diagnostic specificity of 80 per cent (95 per cent confidence interval 66 to 94 per cent). By applying the ELISA to 623 herds in England and 445 herds in Wales, the prevalence of F hepatica infection in England was estimated to be 48 per cent (95 per cent confidence interval 46 to 54 per cent), and in Wales 86 per cent (95 per cent confidence interval 84 to 90 per cent).     

A longitudinal study of seroprevalence and seroconversion of Neospora caninum infection in dairy cattle in northeast Thailand

A long-term study was carried out in 11 dairy herds in the Khon Kaen province of northeast Thailand between August 2001 and November 2004. The objective was to investigate seroprevalence dynamics of Neospora caninum infection in the herds and to demonstrate patterns of seroconversion in individual cattle. Each herd was visited once a year, in total four times, and sera from cattle > 3 months of age and farm dogs as well as a sample from the bulk milk were collected. All samples were analysed for presence of specific antibodies by an N. caninum iscom ELISA. The overall percentage of antibody-positive cattle was constant and varied only between 10 and 13% over the 4 years, but the variation in within-herd seroprevalence between herds was substantial. Two herds had > or = 20% seropositive animals at all samplings and consistently high bulk milk OD, whereas two herds had no seropositive animal at the last two samplings and low bulk milk OD. Five herds had a decreasing trend of within-herd seroprevalence, whereas the remaining six herds had a higher portion of test-positive individuals at the end of the study. A total of 424 individuals were sampled more than once; 344 (81%) and 32 (8%) were consistently antibody-negative and antibody-positive, respectively. The proportions of animals that changed from being seronegative to seropositive and from being seropositive to seronegative between the years were 3.9-4.6% and 19-39%, respectively. Apparent vertical and horizontal transmission rates were 58% (95% CI; 44-71%) and 5% (95% CI; 3-7%), respectively. In conclusion, the overall percentage of N. caninum antibody-positive cattle was constant over the years, but the within-herd seroprevalence varied substantially between the herds. Seroconversions were likely to occur in individual cattle although most animals had consistent serological status throughout the study.     

Factors associated with the seroprevalence of pseudorabies virus in breeding swine from quarantined herds.

Strategies for the elimination of pseudorabies virus (PRV) from swine herds include test and removal, offspring segregation, and depopulation/repopulation. The prevalence of PRV in a herd is a major factor in selection of the most appropriate strategy. The purpose of the study reported here was to describe the prevalence of PRV in adult swine in PRV quarantined herds in Minnesota, and to determine herd factors associated with the seroprevalence. Questionnaires describing the health history of the herd, management practices, and design of the swine facilities were obtained from the owners of 142 quarantined herds. Blood was collected from 29 finishing pigs over the age of 4 months, up to 29 adult females, and all herd boars. Factors considered to be significant in a bivariate analysis were combined in a stepwise multiple logistic regression analysis. The prevalence of PRV-seropositive adults in each herd was bimodally distributed among the 142 herds. In 42 (30%) of the herds, none of the females tested was seropositive, which represented the lower mode. At least 90% of the adults tested were seropositive in 30 (21%) of the herds and represented the higher mode. The odds of the breeding swine of a given herd having a PRV seroprevalence of greater than or equal to 20% as compared with having a seroprevalence of less than 20% was 1.654 times higher per 50 adults in the herd, 13.550 times higher if the finishing pigs were seropositive, 2.378 times higher if sows were housed inside during gestation, and 1.481 times lower per number of years since the imposition of quarantine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Actinobacillus pleuropneumoniae in Thai pig herds. Prevalence of serum antibodies and relation to performance

The aim of the study was to investigate the prevalence of Actinobacillus pleuropneumoniae infections in market weight pigs in Thailand. ELISA systems employing purified lipopolysaccharide antigens were used to detect antibodies in 549 serum samples collected from pigs of 22 herds. Relevant cut-off values were established from three herds defined seronegative. Serum antibodies were detected to all serotypes except serotype 10. Almost 60% of the samples were seropositive to at least one serotype and 45% of the pigs were seropositive to more than one serotype. Antibodies to the cross-reacting serotypes 1, 9 or 11 were found in 29% of the pigs. Other common serotypes included the cross-reacting serotypes 3, 6 or 8 (26% seropositive pigs) and serotype 5a (also 26%). Antibodies to serotypes 2, 5b and 12 were low in prevalence (<10%). Three herds were regarded to be seronegative and six to have a low pathogen load with respect to the prevalence of seropositive pigs. The remaining 13 herds had a high incidence of pigs with antibodies to A. pleuropneumoniae, dominated by serotypes 1-9-11 and 5a (n = 6), serotypes 3-6-8, and 5a (n = 4) or 1-9-11, 3-6-8, 5a and 4-7 (n = 3). A low pathogen load with respect to A. pleuropneumoniae, as well as small herd size and age-segregated rearing, tended to improve the performance of growers.     

Increasing prevalence of Coxiella burnetii seropositive Danish dairy cattle herds

A study based on bulk tank milk samples from 120 randomly selected dairy cattle herds was conducted to estimate the prevalence of Coxiella burnetii seropositive dairy herds, to describe the geographical distribution, and to identify risk factors. Using the CHEKIT Q-fever Antibody ELISA Test Kit (IDEXX), the study revealed a prevalence of 79.2% seropositive herds, 18.3% seronegative herds, and 2.5% serointermediate herds based on the instructions provided by the manufacturer. Multifactorial logistic regression showed statistically significant associations (P < 0.01) between C. burnetii seropositivity and increasing herd size (OR = 1.02 per cow increment) and increasing regional average number of cattle per dairy herd (OR = 1.02 per animal increment). Herds >150 cows had 17.9 times higher odds of testing positive compared to herds <80 cows. The regional average number of cattle herds per square kilometer was borderline significantly related to the occurrence of seropositive dairy herds (P = 0.06). The results indicate an increased prevalence of seropositive dairy herds since the previous survey in 2008 and an adverse impact of increasing herd size and cattle density on the risk of seropositivity.     

Culling decisions of dairy farmers during a 3-year Salmonella control study

Salmonella enterica subsp. enterica-serotypes lead to periodically increased morbidity and mortality in cattle herds. The bacteria can also lead to serious infections in humans. Consequently, Denmark has started a surveillance and control programme in 2002. The programme focuses on Salmonella Dublin which is the most prevalent and most persistent serotype in the Danish cattle population. A field study in 10 dairy herds with persistent Salmonella infections was carried out over three years to gain experience with control procedures including risk assessment, targeted control actions and test-and-cull procedures. From autumn 2003 until end of 2006 quarterly milk quality control samples from all lactating cows and biannual blood samples from all young stock above the age of three months were tested using an indirect antibody ELISA. The most recent and previous test results were used to categorise all animals into risk groups. These risk groups and all individual ELISA-results were communicated to the farmers as colour-coded lists four to six times per year. Farmers were advised to manage the risk of Salmonella transmission from cattle with repeatedly high ELISA results (flagged as "red") or cows with at least one recent moderately high ELISA result (flagged as "yellow") on the lists. Risk management included, e.g. culling or separation of the cows at calving. We analysed culling decisions using two models. For heifers a hierarchical multivariable logistic model with herd as random effect evaluated if animals with red and yellow flags had higher probability of being slaughtered or sold before first calving than animals without any risk flags. For adult cows a semi-parametric proportional hazard survival model was used to test the effect of number of red and yellow flags on hazards of culling at different time points and interactions with prevalence in the herd while accounting for parity, stage of lactation, milk yield, somatic cell count and the hierarchical structure of the data with animals clustered at herd level. This study illustrates how investigation of culling decisions made by herd managers when they have access to test-status of individual animals and overall apparent prevalence during control of an infection can lead to useful new knowledge. Overall herd managers were more likely to cull cattle with increasing number of yellow and red flags than animals with no flags. However, cattle were more likely to be culled with yellow and red flags during times with low or medium high within-herd seroprevalence than at times with high seroprevalence. These results are valuable knowledge for modelling and planning of control strategies and for making recommendations to farmers about control options.