Jens Frederik Agger

Maximum-likelihood estimation of sensitivity and specificity of ELISAs and faecal culture for diagnosis of paratuberculosis.

The accuracy of three diagnostic tests for paratuberculosis was evaluated using maximum-likelihood estimation of sensitivity and specificity. We also explored the variety of estimates that can be obtained if the tests are to be used in populations of different composition with regard to infection and disease states. Two enzyme-linked immunosorbent assays (ELISAs) were evaluated separately with the faecal culture (FC). The study was carried out as a cross-sectional field study to cover all likely states of infection with Mycobacterium avium subsp. paratuberculosis.The three basic assumptions for the maximum-likelihood technique were evaluated to validate the results. Our accuracy estimates for the ELISAs were not very different from those previously published, but those for faecal culture differed if a different cut-off value was chosen for the ELISA. If faecal culture was used for screening in a Danish dairy region where the median ELISA reading was a measure of the general disease situation, the sensitivity of the faecal culture was 20-25%. If faecal culture was used as a confirmatory test on cows with a high ELISA reading (and thus high level of antibodies), the sensitivity of the faecal culture would be in the range 60-70%. These results emphasise the importance of the composition of a target population before selecting a specific diagnostic test for a given purpose. We concluded that faecal culture is useful for confirmation but not for screening purposes.

Prevalence of Coxiella burnetii antibodies in Danish dairy herds.

During recent years in Denmark higher rates of antibodies to Coxiella burnetii have been detected in animals and humans than previously reported. A study based on bulk tank milk samples from 100 randomly selected dairy herds was performed to estimate the prevalence and geographical distribution of antibody positive dairy herds. Using the CHEKIT Q-Fever Antibody ELISA Test Kit (IDEXX), the study demonstrated a prevalence of 59% antibody positive herds, 11% antibody intermediate herds and 30% antibody negative herds based on the instructions provided by the manufacturer. The geographical distribution does not indicate a relationship between the regional density of dairy farms and the prevalence of antibody positive dairy farms. The result supports the hypothesis of an increase in the prevalence of positive dairy herds compared to previous years.

Reported behaviour problems in pet dogs in Denmark: age distribution and influence of breed and gender

Abstract In the period 1987–1991 the consultant service established by the Danish Animal Welfare Society and the Danish Civil Dog Training Association reported 3975 problems in relation to pet dogs in Denmark. With nine categories of problem behaviour a total of 2719 problems were recorded in 2238 dogs. The data were analysed for the influence of breed, gender and age on the risk of developing behaviour problems. The analysis was designed as a case-control study using two control groups: (1) dogs registered by Danish Kennel Club in a 5-year period and (2) dogs treated at The Royal Veterinary and Agricultural University, Copenhagen, Denmark in a 4-month period. Thirteen breeds or breed groups including mixed breeds were compared with a reference group consisting of Labrador Retrievers. Compared with the reference group, Alsatians seemed to have higher risks of aggression towards other dogs, aggression towards strangers and general anxiety. For Cocker Spaniels higher risks of aggression towards the owner, aggression towards strangers and indoor urination/defecation were found. Collies seemed to have higher risks of aggression towards strangers, indoor urination/defecation and general anxiety. Furthermore, a higher risk of general anxiety was found in Poodles and Fox Terriers. Generally, Dachshunds, a group consisting of all terriers excluding Fox Terriers and mixed breeds, seemed to have a low risk of behaviour problems. Compared with females, males seemed to have a lower risk of general anxiety and a higher risk of problems related to lack of training and all kinds of aggression. About 80% of the behaviour problems were reported within the first 3 years of life. Only 5.5% of the dogs were suggested to be or were in fact euthanized.

Incidence of clinical mastitis in Danish dairy cattle and screening for non-reporting in a passively collected national surveillance system.

Dairy herds from three counties in Denmark (n=2144) were monitored for a 1-year period to measure the incidence rate (incidence-density) of clinical mastitis. Two different screening methods were evaluated to remove herds from the database for which the herdsman and veterinarian were suspected of under-reporting the mastitis cases which had occurred. One method was based upon agreement between clinical mastitis reports and measures of somatic cell counts of >1 million cells per ml. A second method was based upon agreement between cases reported through the regular disease-reporting system and cases reported on a management questionnaire. Depending upon the method of calculation and screening method used, rates of clinical mastitis varied between 36 and 48 cases per 100 cow-years at risk. The exclusion of herds because of documented non-reporting behavior (screening) resulted in a preponderance of herds with zero or very low incidence of mastitis being removed from the database. Following screening, the frequency distribution of herd mastitis incidence rates became decidedly more symmetrically and normally distributed.

A retrospective study on salmonella infection in Danish broiler flocks

Abstract A retrospective longitudinal study was conducted to identify risk factors associated with Salmonella enterica infection in Danish broiler production. The study was based on information in the antemortem database (AM database) where data were available for all broiler flocks slaughtered over the 2-year period from 1992 to 1993 in Denmark. The AM database contains information collected by the ante-mortem veterinarians, from the slaughterhouses, and from the salmonella examinations carried out at the National Veterinary Laboratory. The epidemiological unit was the individual broiler flock. The salmonella status of the flock was determined by examining the caecal tonsils from 16 3-week-old chickens from each flock. This procedure would detect a salmonella-infected flock, with a probability above 95%, if the prevalence is above 20%. Furthermore, the structure and quality of the collected data have been evaluated. Fourteen variables were selected for analysis by multivariable logistic regression. An increased risk of salmonella infection in the broiler flocks was associated with the biggest hatcheries and feedmill, with an increasing number of houses on the farm, if the preceding flock was infected, and if the flock was reared in the autumn. Additionally, the main variables of the model were analysed by including a random effect at the house level. This resulted only in minor changes of the parameter estimates.

Lameness in tied Danish dairy cattle: The possible influence of housing systems, management, milk yield, and prior incidents of lameness

Abstract Lameness constitutes a group of diseases which have a major impact on the welfare of affected animals, because lameness is usually associated with substantial pain and discomfort and is of long duration. Knowledge of the risk factors for lameness might be used to reduce the incidence of lameness. Therefore, a retrospective longitudinal study was conducted to determine the influence of several risk factors on the incidence of lameness in tied Danish dairy cattle. The information used originated from the Central Danish Disease Recording Scheme and from a questionnaire survey. Disease incidents occurring from 1 month before to 7 months after parturition were considered. To estimate the associations between nine different kinds of lameness in two successive lactations, Fishers exact test was used. To determine the effect of other possible risk factors on foul in the foot (interdigital necrobacillosis) and hock lesions (tarsal cellulitis and its sequelae), multivariable random-effects logistic regression was used. The results indicate that many of the different kinds of lameness interrelate from one lactation to the next. The factors associated with increased risk of foul in the foot were: first parity, summer calving combined with outdoor grazing, use of yoke tie, and high average herd milk production. Risk factors for hock lesions were: breed (Danish Jersey lower than Red Danish and Danish Black and White), first parity, winter calving, use of electric cow trainer, and high average herd milk production.

Coxiella burnetii associated placental lesions and infection level in parturient cows

Cotyledons (n=170) from dairy cattle were analysed for Coxiella burnetii by real-time (rt) PCR targeting the IS1111a and icd genes. Positive cases (n=90) and a random selection of negative cases (n=20) were examined by histology, immunohistochemistry and, if infection level was high, by fluorescence in situ hybridisation. PCR results were compared to bulk tank milk (BTM) antibody levels. Placental infection was detected in cows from herds at all BTM antibody levels. However the likelihood of placental infection was generally higher in herds with intermediate or high BMT antibody levels than in herds with low antibody levels. Histological examination revealed a range of mostly mild cotyledonary changes; C. burnetii infection was only rarely associated with inflammation. This may explain why bovine Q fever is usually not clinically apparent. Nevertheless, infected cattle will shed C. burnetii at calving and this can occur even in herds without BTM antibodies.

Cointegration analysis used in a study of dairy-cow mortality.

A competitive environment forces the farmer constantly to adopt new and more-intensive production methods aiming at lowering costs and increasing yields. At debate is whether this intensification of production has an adverse impact on animal health and welfare. We investigated this issue by using cointegration analysis (a new tool used in time series analysis). We introduce cointegration analysis by applying the method in an epidemiological study of dairy-cow mortality. Two long-run epidemiological relations are identified:(i) a physiological relation (where increasing consumption of concentrates corresponded to increasing milk yield and mortality) and (ii) a physical relation (which illustrated that higher mortality was closely related to a higher growth rate of the average herd size, current investments in dairy farming, and higher milk yield). We concluded that a higher level of physiological stress due to higher yield and concentrate consumption has led to increased mortality. Furthermore, changes in the physical environment due to increased mechanisation and larger herd sizes have contributed to less attention per cow and increased mortality.

Foul in the foot (interdigital necrobacillosis) in Danish dairy cows — frequency and possible risk factors

Abstract Foul in the foot is a disease which has a substantial impact on the welfare of the affected cows and the economic return to the farmer. Factors associated with foul in the foot were evaluated in a retrospective longitudinal study. A total of 9520 Danish dairy cows from 171 herds from Ringkobing County were included in the multivariable analysis. Information was collected between January 1990 and December 1991. The cows incidence risk of foul in the foot was 0.6% during the first month post partum. This was six times higher than in the last month prepartum and in any other month post partum. Almost half (39.9%) of the first treatments for foul in the foot were provided within the first 30 days post partum. Hence, there was a relationship between foul in the foot and calving. The seasonal distribution of all veterinary treatments for foul in the foot showed that in both years approximately half the treatments (46.4% in 1990; 48.8% in 1991) were provided during the summer months June–September. There was no apparent association between total monthly number of veterinary treatments for foul in the foot and precipitation. The association between foul in the foot and the possible risk factors was assessed using logistic-binomial regression with herd as a random effect. The results suggest that Danish Jersey cows have reduced risk of developing foul in the foot during a lactation compared to Red Danish, Danish Black and White, and Danish Red and White cows. First-parity cows had highest risk of foul in the foot, second-parity cows lowest. Loose-housed cows had higher risk of foul in the foot than tied cows. There was a positive association between incidence of foul in the foot and incidence of other lameness than foul in the foot.

Factors associated with Coxiella burnetii antibody positivity in Danish dairy cows

The aim of the study was to identify associations between the level of Coxiella burnetii (C. burnetii) antibodies in individual milk samples and cow and herd level factors in Danish dairy cows. The study, designed as a prospective cross sectional study with follow up, included 24 herds identified by a stratified random sampling procedure according to the level of C. burnetii antibodies in one bulk tank milk (BTM) sample at the beginning of the study. Ten herds were BTM positive, ten herds were BTM negative and four herds had an intermediate level. The samples were tested with an ELISA and results determined as S/P (sample to positive control) values. Three cross sectional studies of all lactating cows within each herd were then conducted during an 11 months follow up period with collection of a total of 5829 milk samples from 3116 cows. Each sample was tested with the same ELISA as used for BTM testing, and cows were considered test positive for S/P values ≥ 40, and otherwise negative. Individual cow information was extracted from the Danish Cattle Database and herd information was obtained from a telephone interview with each farmer. From multivariable logistic regression analysis accounting for hierarchical structures in the data it was concluded that odds for seropositivity increased with Danish Holstein breed, increasing number of parity and high milk protein contents, but decreased with increasing milk yield and high milk fat contents. Cows were at a higher risk during summer than other seasons. Among the herd level factors, herd size, tie stall housing system, quarantine of newly purchased animals and good hygienic precautions taken by the veterinarian before entering into the stable were also significantly associated with reduced odds of C. burnetii antibody positivity. The prevalence of test positive cows was almost constant during the study period in herds which were initially BTM positive and BTM intermediate, whilst the prevalence of positive cows in a few of the initial BTM negative herds changed from almost zero to higher than 60%. This indicates that herd infections last quite long and that test negative herds may convert to positive due to a few latently infected cows or due to transmissions from other herds.