Moniliformin in Norwegian grain.

Norwegian grain samples (73 oats, 75 barley, 83 wheat) from the 2000-02 growing seasons were examined for contamination with moniliformin, and the association between the fungal metabolite and the number of kernels infected with common Fusaria was investigated. Before quantification of moniliformin using ion pairing reversed-phase high-performance liquid chromatography with diode array ultraviolet light detection, all samples were extracted using acetonitrile/water (84/16) and disposable strong anion exchange columns used for clean up. The limit of detection was 40 microg kg(-1). Moniliformin was found in 25, 32 and 76% of the barley, oats and wheat samples, respectively. The maximum concentrations of moniliformin in barley, oats and wheat were 380, 210 and 950 microg kg(-1), respectively. At the same time, the prevalence and infection level of the moniliformin-producing F. avenaceum/arthrosporioides was as high as 100 and >53% on average, respectively. Moniliformin concentrations were significantly correlated to the variables grain species, growing season and infection with F. avenaceum/arthrosporioides and F. culmorum. The survey indicates that the prevalence of moniliformin in Norwegian grain is high, especially in wheat. On the other hand, field conditions in Norway do not seem to favour contamination of grain with high levels of moniliformin.

Factors affecting the herd level of antibodies against Mycobacterium avium subspecies paratuberculosis in dairy cattle.

A case-control study was made of Norwegian dairy herds with high and low herd levels of antibodies against Mycobacterium avium subspecies paratuberculosis. A high proportion of the herds had a considerable number of seropositive cows, and environmental and management factors were examined for possible associations with the high serological levels of antibodies. The most important appeared to be: geographical location, red deer (Cervus elaphus) gaining access to the pastures for cattle, the observation of wild birds in the feed storage, and herds sharing common pasture with other herds of cattle. However, diagnostic tests showed that none of the animals in the case herds was infected with M a paratuberculosis.

Influence of bovine manure as fertilizer on the bacteriological quality of organic Iceberg lettuce.

AIM: To investigate the bacteriological quality, and the occurrence of selected pathogenic bacteria from organically grown Iceberg lettuce fertilized with bovine manure in the form of compost, firm manure and slurry in a 2-year field trial. METHODS AND RESULTS: Samples of soil, fertilizer, fertilized soil, seedlings and lettuce were analysed for aerobic plate counts (APC), thermotolerant coliform bacteria (TCB), Escherichia coli, E. coli O157:H7, Salmonella spp. and Listeria monocytogenes. No difference in bacteriological quality could be shown in lettuce at harvest, however, APC varied significantly from year to year in the study. The various treatments gave significantly different APC and numbers of TCB isolated from fertilized soil. Escherichia coli O157:H7 was isolated from firm manure and slurry, and soils fertilized with the respective fertilizers the second year, but were not recovered from the lettuce. CONCLUSIONS: No difference in bacteriological quality could be detected in lettuce at harvest after application of various types of manure-based fertilizers grown under Norwegian conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: The results may indicate that the use of manure does not have considerable influence on the bacteriological quality of organic lettuce. However, others have suggested that there is a risk by using manure. There is a need for more research in the field.

Cardiomyopathy syndrome in farmed Atlantic salmon Salmo salar: occurrence and direct financial losses for Norwegian aquaculture.

Cardiomyopathy syndrome (CMS) was first diagnosed in the mid-1980s in farmed Atlantic salmon in Norway, and later also in Scotland and the Faeroe Islands. In Norway the number of diagnosed cases increased from 25 to 103 in the period from 1998 to 2001 according to the National Veterinary Institute (NVI) records. Very little is known about the causes of the disease and there is no documentation of its impact on the farmed salmon industry. This field survey was performed to collect information on occurrence, risk factors and the economic importance of CMS in sea farmed Atlantic salmon Salmo salar in Norway. Data were collected in January 2001 from a total of 174 groups of farmed salmon which had been previously transferred to sea during 1999 and 2000. Approximately 11.5% of all groups of salmon in our study experienced cases of CMS. Affected fish were presumably in generally good condition prior to time of death. In fish which had completed the seawater production cycle, CMS occurred more than 1 yr (median 395 d, >2 kg body weight) after seawater transfer. In fish transferred into the sea during autumn 2000 which had not completed the seawater cycle during the study period, CMS was diagnosed at a weight as low as 700 g. Although sudden death is characteristic, CMS may be regarded as a chronic disease, with moderately elevated mortality rates at site level. Affected groups showed significantly increased mortality, causing a direct annual financial loss for the industry of Euros 4.5 to 8.8 million on fish farms. Preventive prescheduled slaughtering of salmon, which is performed on many affected farms, may be too costly when done too early.

Factors associated with mortality in Norwegian broiler flocks.

Our aim in this longitudinal study (covering years from 1996 to 1999) was to use data regularly recorded in a production database, to identify farm- and flock-level factors associated with cumulative mortality in broiler flocks during: (a) the 1st week after housing and (b) the rest of the growout (2nd to 5th week). A total of 1664 broiler flocks kept in 132 broiler farms were included. The average weekly cumulative mortality was 1.54% (95% CI: 1.46, 1.62%) during the 1st week and 0.48% (95% CI: 0.47, 0.49%) during the rest of the growout. The final least-squares regression model of cumulative mortality during the 1st week identified the following significant factors: study year, flock size, stocking density, use of paper underlay for feeding during the 1st week, and the interaction terms between type of ventilation, drinking system and floor insulation. The final model for the 2nd to 5th week demonstrated that the factors age of the broiler house, heating system and control system for the air intake were associated with cumulative mortality, but the effects of the two latter variables were significantly modified by age of the broiler house. A significant difference in mortality between flocks delivered from various hatcheries was found in both analyses. Our results suggest that changes in several housing factors and management routines might reduce the mortality losses, but the relationship depends on the stage of production.

A field study of naturally occurring specific antibodies against Clostridium perfringens alpha toxin in Norwegian broiler flocks.

Necrotic enteritis (NE), a disease associated with high numbers of the intestinal bacterium Clostridium perfringens, is common in intensive broiler production. Antimicrobial feed additives may control the disease, but their use is now being questioned in many countries. A field study was undertaken at the end of 1997 to study the level of naturally occurring specific humoral immunity against phospholipase C (PLC; C perfringens alpha toxin) in Norwegian broiler flocks. Blood samples were collected at hatch from 61 study flocks, and the sampling was repeated for 56 of the same flocks at processing. The level of specific antibodies against PLC was analyzed in an enzyme-linked immunosorbent assay (ELISA) test. Data on production performance and weekly mortality were recorded. The relationship between the age of the hens and the level of specific maternal antibodies in the progenies was studied. The association between the level of the maternal antibodies and the production performance, including mortality, was analyzed. The level of specific antibodies against PLC in day-old broiler flocks was relatively high and varied considerably compared with the levels in the broilers at processing. The progenies from the oldest hens had significantly higher levels of specific antibodies than the chicks from younger hens. No outbreak of NE occurred during the study period, making it impossible to analyze the association between naturally occurring specific immunity against PLC and the occurrence of the disease. However, the results showed that the flocks with high titers of specific maternal antibodies against PLC had lower mortality during the production period than flocks with low titers.

An epidemiological study of cataracts in seawater farmed Atlantic salmon Salmo salar.

Cataracts in farmed Atlantic salmon have been known for many years, but the aetiology and importance of the disease have not been clarified. A cross-sectional field study of 51 cages of Atlantic salmon at 49 randomly selected sea sites was performed during the summer of 1998. The target population was spring and autumn entry groups of the 1997 generation salmon. Approximately 15 fish from each cage, altogether 777 fish, were autopsied by the same person. Each eye of the fish was scored for cataracts on a scale from 0 to 4 using an otoscope lamp with magnification. The weight and length of each fish were measured. The prevalence of cataracts was 83 % and 79% in spring entry groups and autumn entry groups, respectively. The overall mean cataract index (mean score of both eyes) was 1.23, being significantly higher in the spring entry groups (1.36) than the autumn entry groups (0.85). The final results in the spring entry groups showed that the fish groups with higher weight at sea transfer also had a higher cataract index at inspection. The risk of development of cataracts varied significantly among the offspring from the 5 strains represented in the study. Fish from sites located in 2 counties in the southern part of Norway had a significantly higher cataract index than fish farmed in the northernmost county in the study. For the autumn entry groups none of the explanatory variables was significant. In the spring entry groups a significant negative relationship was observed between the cataract score and the weight of the fish at the time of inspection (Pearson's r = -0.17), while the corresponding correlation for the autumn released groups was r = -0.10. Among the spring entry groups the average weight of the fish with the highest cataract score was estimated to about a third of the weight of the fish with no visible cataracts.

A case-control study on scrapie in Norwegian sheep flocks.

Scrapie first was detected in indigenous sheep in Norway in 1981, and from 1995 to 1997 an increase in the number of flocks with scrapie cases was recorded. These flocks were mainly in one geographical region. A study to identify risk factors for scrapie was conducted. The study had three frequency-matched controls selected for every case within the same Veterinary District. A questionnaire was submitted to 176 sheep flocks (42 had been scrapie flocks). The data obtained by the questionnaire were linked to data collected from governmental and industry registers. After imputing missing data using single random imputation, the statistical analysis was performed using multivariable conditional logistic regression. Purchase of female sheep from scrapie flocks, sharing of rams, or sharing of pastures between different flocks were the risk factors associated with the occurrence of scrapie. Of factors potentially sustaining and promoting the infection in the flock, number of winter-fed sheep, number of buildings for housing sheep, rams and ewes shared room during mating period and increase in the flock size were associated with scrapie. We interpret these findings to show that factors involving transfer of sheep between flocks or direct contact between sheep of different flocks are important for the spread of scrapie. Management factors are important for the development of scrapie. However, it was not possible to discriminate between the different management factors in this study at the flock level. Also, factors indicating awareness and interest of the farmer (as well as willingness to contact a veterinarian for diseased sheep) were related to the detection of scrapie in the flock.

The effect of an outbreak of respiratory disease on herd-level milk production of Norwegian dairy farms.

This study was done to evaluate the effect of an outbreak of acute respiratory disease associated with bovine respiratory syncytial virus (BRSV) on the daily milk yield per cow in Norwegian dairy-cattle farms. Retrospective data from 184 dairy herds located in two neighbouring veterinary districts during the study period (December 1994-May 1995, during which an epidemic of acute respiratory disease associated with BRSV occurred in this area) were analysed. Data on the bulk-milk deliveries and the date of the outbreak were collected at herd level, whereas information on calving dates and parity was collected at cow-level. The effect of the herd outbreaks on the daily milk yield was analysed with a repeated-measurement approach. The average daily milk loss was estimated to be 0.70kg per cow for 7 days after a herd outbreak (compared with the period >1 week prior to an outbreak), adjusted for the herd-level lactation stage, parity and their interaction term. We consider the estimated milk loss associated with a herd outbreak of epidemic respiratory disease to be of minor importance.

An epidemiological study of the hatchability in broiler breeder flocks.

The aim of the present retrospective longitudinal study was to identify factors that significantly influenced the hatchability observed during the period from 1996 to 1998. Data from 112 Ross 208 breeder flocks in 39 breeding farms were included in a repeated-measures analysis with the flock-level "interval-specific" hatchability of the eggs as outcome variable. The overall mean of interval-specific hatchability in the study was 75.9% (95% confidence interal: 75.3 to 76.6%). The hatchability was influenced by the storage time from lay until incubation and whether the farmers delivered floor eggs for hatching. The method used for disinfecting the hatching eggs and the flock average slaughter weight were significantly associated with the hatchability. A significant effect of time (production year) and flock size were also found on the hatching results. The results showed that several factors may influence the hatchability, the most detrimental being long egg storage time. With an optimization of the capacity and administration of the hatcheries, it would be possible to improve the hatching results.

A retrospective analysis of the infectious bovine rhinotracheitis (bovine herpes virus-1) surveillance program in Norway using Monte Carlo simulation models.

Serological surveillance for antibodies against bovine herpes virus type I (BHV-1) which causes infectious bovine rhinotracheitis and infectious pustular vulvovaginitis has been carried out since 1992 in Norway. Since 1993 (when a single infected herd was detected) all bulk-milk and pooled-serum samples have been negative for BHV-1 antibodies. This paper describes the use of Monte Carlo simulation models for the analysis and interpretation of the results of the surveillance and provides support for the contention that the Norwegian cattle population is not infected by BHV-1.

Occurrence and characterization of Escherichia coli O157 isolated from cattle in Norway.

Faecal samples from 504 imported beef cattle were screened to investigate the occurrence of Escherichia coli O157. The results were compared with those from a previous screening of Norwegian dairy cattle, and the occurrence was found to be higher in the imported beef cattle. The E. coli O157 isolates from the previous and present studies were characterized for the genes encoding for shigatoxin 1 (stx1), shigatoxin 2 (stx2), the intimin protein (eae) and the flagellar protein H7 (fliC) using PCR analysis, pulsed-field gel electrophoresis (PFGE) with the restriction enzyme XbaI, and bacteriophage lambda RFLP analysis using the PvuII restriction enzyme. The isolates from the dairy and beef cattle could be distinguished by the profiles of the toxin genes and by PFGE patterns. Whether the importation of animals in itself should be regarded as a risk factor for the occurrence of E. coli O157, or whether other management factors contribute to the differences in carrier rates compared to the previous study on domestic cattle, is discussed.

Risk factors for Marek's disease and mortality in white Leghorns in Norway.

A prospective longitudinal field study was conducted in the period from January 1994 to January 1996 to analyse the relationship between some selected risk factors in the growing and laying periods and (1) the flock-level occurrence of Marek's disease (MD) during the period from 16 to 32 weeks of age and (2) the cumulative mortality during the same period. A total of 171 layer flocks in 102 egg-production farms were included in the statistical analyses.A logistic regression (with strain of layer and vaccination program against MD as fixed effects) of flock-level MD-status during the first 16weeks of the laying period was conducted. Of the risk factors investigated, "multi-age management" and "housing system" were significantly associated at the rearing farm, and "number of hens in each cage" at the egg-production farm. Flocks kept in single-age facilities had a lower risk of MD than flocks housed in farms with multi-age management. The odds of MD were larger for flocks housed on a litter floor in the rearing farms compared to flocks housed in battery cages. At the egg-production stage, flocks kept in battery cages housing more than three hens were at greater risk of MD than those held in cages for three hens or less.A weighted least-squares regression (with strain of layer and flock-level MD-status as fixed effects) of cumulative mortality during the period from 16 to 32weeks of age was also run. The same risk factors (with the same directions of effects) and "size of the rearing farm" were included in the final model of mortality. Chicks reared in medium-sized farms were at higher risk of dying than those coming from either small or large rearing farms. Our results confirm the importance of preventing chicks from being exposed to MD-virus during the rearing period, to reduce the risk of MD-outbreaks (and thereby, mortality losses) during the early stage of the egg-laying period.

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

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

Risk factors for epidemic respiratory disease in Norwegian cattle herds.

An epidemic of acute respiratory disease associated with bovine respiratory syncytial virus (BRSV) occurred during the winter and spring of 1995 in two neighbouring veterinary districts in the south-eastern part of Norway. The objective of this study was to describe the time course of the outbreak associated with BRSV in the cattle herds, and to determine the association between selected herd factors and the risk of experiencing a herd outbreak of acute respiratory disease. Data from 431 cattle herds on the dates of disease occurrence, location of the farms, herd size, age profile and production type were collected retrospectively for 1995. The risk of acute respiratory disease occurring in a cattle herd was related to the herd size as well as the type of production, with an expressed interaction between these two variables. From the Cox proportional-hazards model, the risk of a herd outbreak in a mixed herd of 20 animals was estimated to be 1.7-times greater than in a dairy herd and 3.3-times greater than a beef herd (reference category) of a comparable size. On increasing the herd size to 50 animals, the risk increased 1.3-fold for a mixed herd, 3.3-fold for a dairy herd, and 2.1-fold for a beef herd, compared to the risk for a corresponding type of herd of 20 animals.

A Monte Carlo simulation model for assessing the risk of introduction of Gyrodactylus salaris to the Tana river, Norway.

The Tana river in northern Norway, the most productive salmon river in Europe, is free of Gyrodactylus salaris. Currently there is one salmon farm in operation on the Tana fjord. Because of the strong association between stocking of rivers with salmon and infestations with G. salaris there is national and international concern that the existing farm might lead to the introduction of the parasite to the Tana river. In response to these concerns a quantitative analysis of the risk of introduction of G. salaris to the Tana river was undertaken. A scenario tree, the Monte Carlo simulation model and results of the simulations including sensitivity analyses are presented and discussed. Results show that the probability of introduction of G. salaris to the Tana river via transfer of smolt to the existing salmon farm is extremely low primarily due to the low probability that the transferred smolt become infested. The total risk was very sensitive to changes in the salinity of the water at the sea site.

A longitudinal field study of mortality and Marek's disease in Norwegian and imported white Leghorns.

High mortality during the first part of the laying period was observed in Norwegian White Leghorns during the period 1988-1992. A longitudinal field study with repeated measurement of cumulative mortality was undertaken in the period from January 1994 to January 1996 to investigate (1) the mortality and susceptibility to Marek's disease (MD) in the Norwegian strain (NB41) compared to two imported layers, (2) the effect of MD on the total cumulative mortality in the period from 16 to 32 weeks of age in White Leghorn flocks, and (3) the effect of MD as judged by repeated measurement of cumulative mortality in the same period. All five layer hatcheries and 67% of the pullet-rearing farms in Norway participated in the field study. The egg-production farms were sampled by convenience. Recordings for the whole period were completed for 169 flocks in 101 farms. The statistical analyses were performed using both a general fixed-effects linear model and a mixed model with repeated measurements, with total flock-level cumulative mortality and flock-level cumulative mortality in four-week intervals as outcome variables, respectively. The overall cumulative flock-level incidence of MD was 12% (24% and 8% in NB41 and Lohmann White, respectively). MD was not recorded in any of the Shaver White flocks. A significant difference (p < 0.001) was found in (1) total cumulative mortality: 8.2% in the NB41 and 5.0% in the imported layers, and (2) 'interval-specific' cumulative mortality: 0.36% in the NB41 and 0.15% in the imported birds. A strong relationship was also demonstrated between MD and repeated measurements of 'interval-specific' cumulative mortality (p < 0.001) but not when cumulative mortality was used as an overall measure for the whole laying period (p = 0.11). The results from the repeated-measures analysis also indicated a stronger effect of MD on flock-level 'interval-specific' cumulative mortality in the NB41 than in the imported hens. The different cumulative mortality and susceptibility to MD observed in the NB41, compared to the imported hens, shows that the farmers will be able to reduce their losses by replacing the NB41 strain with one of the imported strains.

A space-time cluster investigation of an outbreak of acute respiratory disease in Norwegian cattle herds.

Outbreaks of acute respiratory disease occurred in several cattle herds in the south-east regions of Norway during the winter and spring of 1995. The present study was conducted to investigate the temporal and spatial dynamics of the occurrence of acute respiratory disease between January and April 1995 in the affected cattle herds, in two neighbouring counties in Norway. This was done to assess the possible role of an infectious agent in these outbreaks, as well as to investigate the possibility of transmission between neighbouring herds. During the study period, a total of 190 (19.8%) outbreaks occurred in 955 cattle herds located in the defined study area. Descriptive maps of the spatial and spatio-temporal patterns of the outbreak were generated, and two different statistical tests of space-time interaction (the Knox test and k-nearest neighbour test) and a cluster-detection test (the space-time scan statistic) were used. The results of all the space-time interaction tests strongly suggested that the case herds were clustered in time as well as in space. In addition, the space-time scan statistic defined the most-likely cluster to be located within the second veterinary district (Toten where the disease occurred) during 9-15 weeks in 1995. The relative risk of a herd being infected inside the most-likely cluster compared with the surrounding study area was estimated to be 3.59 (p=0.001). The transmission rate between neighbouring farms therefore appeared to have been higher within this cluster than in the surrounding study area. This study supports the hypothesis that one common source of infection was involved in the outbreaks during the study period.

Statistical aspects of fish vaccination trials.

Vaccine trials are performed to measure the efficacy of vaccines or vaccination strategies. The statistical aspects pertain both to design and analysis of such trials. In experimental trials, the design should ensure that the groups to be compared are equal in all respects except for the factor to be assessed. This is achieved by proper randomisation procedures. The diagnosis of cases should as far as possible be carried out without knowledge of vaccination status (blinding). If the administration of a vaccine per se is considered to influence the outcome, a similar administration of placebo in the control group should be considered. The required sample size will depend on a specified significance level, a specified power, and on the magnitude of the effect one wants to detect. If the cumulative numbers of cases in vaccinated and unvaccinated groups are registered at the end of the observation period, the effect can be measured by the risk ratio, risk difference or the relative percent survival. If the estimation is based on a fish-time approach and the presumption of constant rate of outcome over time is fulfilled, the rate ratio or the rate difference can be estimated. If the rate is not constant, the life table would be a method of choice. In the statistical analysis of the vaccination effect it is important to consider the assumptions on which the statistical tests are based. Proper choice of the experimental and statistical units in the trials is crucial. If a trial is set up with the individual fish as the statistical unit, adjusting for dependence (cluster effect) between the units may be indicated. If possible, the vaccine effect should be given by the point estimate and the confidence intervals. The statistical aspects of fish vaccination trials are based on general principles for controlled clinical trials, but they are also influenced by characteristics connected to the fish population and the experimental conditions.